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Trouble-shooting Personal Computer Systems

1. Introduction

This document gives some basic advice about troubleshooting your personal computer system. It is not intended to be a complete guide to all possible problems. However, even if you are a non-technical person, there are some simple steps you can take to try and diagnose a problem. Even if you don't manage to solve a problem yourself, hardware and software suppliers and help desk staff will be in a much better position to help you if you have managed to perform some basic troubleshooting procedures before you contact them.

2. Step 1 - Don't Overlook the Obvious!

Many computer problems have very basic, simple causes. Always check the obvious before assuming it must be a complicated and obscure problem. Some examples of this are:

2.1. Cables

Some of the most common problems are caused by cables which are loose, faulty, or which were strained/unplugged by the office cleaners, or borrowed by the person in the next room while you were on holiday. This can result in equipment that appears dead, screens that are blank or have strange colours, or workstations that can't contact the network. For example:

  • The power cable(s) have been unplugged from the mains, or are not pushed in firmly enough into the back of the unit.

  • The data cable between the display and computer is loose or unplugged.

  • The cable between the computer and the network socket is loose or unplugged.

  • The cable between your modem and the phone socket is faulty or of the wrong type for the UK.

  • A vital cable is missing or plugged into an incorrect socket.

If a faulty cable is a possibility, try out a substitute if one is available - ideally one that is known to be working.

2.2. Controls

The various controls on the computer, display, sound system etc. may have been changed by another user. For example your screen unit may power up and the cables are all OK but there is still nothing on the screen. The cause could be that the monitor's brightness and/or contrast control have been turned right down and just need re-adjusting.

Another (real-life!) example: many computers provide the mains power for their accompanying display - this means that the display's own power switch normally can be left in the "on" position and the computer's own power switch used to turn both computer and display on or off. Someone else using such a computer might "helpfully" turn off the display's power switch so that when the system is next turned on, the display appears dead until someone notices that the display needs switching on.

3. Step 2 - Narrow Down the Problem

The next step in diagnosing a problem is to try and narrow down the location of the problem and the context in which it occurs. For example it may only happen with a particular program, or with a particular user, or when processing a certain document, or at a particular location or at a certain time of day. Examples of narrowing down the problem in some common scenarios are illustrated below.

3.1. Scenario A - A Printing Problem

You can't access your printer - does the fault lie in the computer or the printer or the cable in between?

  • Does a different cable (preferably one know to work elsewhere) fix the problem?

    • YES - your original cable was faulty or not connected properly.

    • NO - then...

  • Does the printer work with a different computer?

    • YES - the problem is probably within the computer

    • NO - the problem is probably within the printer.

  • Does a similar printer work with your own computer (using the same printer driver)?

    • YES - the problem is probably with the original printer

    • NO - the problem is probably within the computer.

If the problem seems to be within the computer:

  • Is the problem confined to just one application?

    • YES - the problem is with the installation/configuration of that particular program.

    • NO - then...

  • On a PC Windows system, is printing possible from the MS-DOS command prompt (e.g. via a command such as: COPY C:\AUTOEXEC.BAT LPT1: )?

    • YES - the hardware is OK and the problem may be in Windows printer-driver installation/configuration.

    • NO - there may be a problem with the computer's printer port.

If the problem seems to be with the printer:

  • Does it print its internal test page?

    • YES - there may be a fault with the printer's communication port

    • NO - the printer may have its paper/ink/toner incorrectly inserted or may have more serious internal problems.

3.2. Scenario B - A Communications Problem

You are running Netscape Communicator on a workstation connected to a college ethernet socket. You can't access a particular web page, for example one at a site in the United States. The problem could be in:

  • Netscape Communicator installation/configuration

  • Workstation's communication software installation/configuration

  • Workstation's communication hardware

  • Cabling between workstation and local network point

  • Cabling between local network point and network hub

  • Communications link between local college/departmental network and local central network

  • Communications link between local central network and external UK national network

  • Communications link between UK national network and US national network

  • Communications link between US national network and remote US site

  • The server at the remote US site

Although some of these factors are clearly outside your control, it should still be possible to narrow down the problem. For example:

  • Can you access other US sites successfully, e.g.

    • YES - the problem is at the remote site

    • NO - then...

  • Can you access any UK sites, e.g.

    • YES - the problem may be with the transatlantic link (or with the web-cache if you have a Netscape proxy configured for non-UK sites)

    • NO - then...

  • Can you access any local sites, e.g.

    • YES - the problem may be with the link between the local central network and the UK national network.

    • NO - then...

  • Can you access any sites within your department, e.g. a departmental web server? If you have Windows 95/98/NT, can you browse the Network neighbourhood and see other local machines listed?

    • YES - the problem may be with the link between your college/departmental network and the local central network.

    • NO - then...

  • Can you successfully use other communications such as Telnet, FTP, or a different web browser.

    • YES - the problem may be a Netscape configuration setting

    • NO then...

  • Does your machine work if you use a different cable or network socket which are known to be OK?

    • YES - you have a faulty cable or network socket.

    • NO - then the problem is probably with your communications software installation or configuration. How you proceed from here depends on what type of system you have. For example...

  • If you have Windows 95/98/NT, does the System Control Panel's Device Manager entry for your network adapter report a problem?

    • YES - there is a problem with your network adapter.

    • NO - then...

  • Does the Network Control Panel have a TCPIP protocol entry and are its properties configured correctly?

    • NO - Add a TCPIP entry and configure its properties using the address information obtained from your unit's IT Officer.

    • YES - then...

  • Use the Start/Run option and enter the command: WINIPCFG - does this display all your address information correctly?

    • NO - there is a problem in your TCPIP configuration. You could try removing the TCPIP entry from the Network Control Panel and re-adding/re-configuring it.

    • YES - seek help!

3.3. Scenario C - An Email Problem

If you have a problem using your email client, the fault could be in your workstation's email client configuration, or in its general communications setup, or with your account on the remote mail host, or even a general problem with the mail host itself.

  • Do other communications programs such as Netscape or Internet Explorer work?

    • NO - you probably have a general communications problem.

      • If you are connected to the campus ethernet system, see the last 4 steps of the previous section.

      • If you are a dial-up user, check your dial-up configuration. If you have a new or recently changed password, your dial-up configuration may need updating to include this information.

    • YES - then..

  • Is the problem only with sending mail?

    • YES - then...

      • check the SMTP host on your email client's configuration screens - set it to

      • check your own email address on your email client's configuration screen. It should be of the form: e.g. - it must not contain spaces, accented characters etc. If your client allows you to define a "Return address" this should normally be left blank.

      • Check the recipient's email address carefully. Try sending a message to yourself.

      • Check your time-zone is set correctly - on Macs, use the Map control panel; on Windows 3.x add the line SET TZ=GMT0BST to your AUTOEXEC.BAT file.

    • NO - then...

  • Is there a problem with both sending AND receiving mail?

    • YES - then...

      • Check your mail-host and SMTP entries on your mail client's configuration screen.

      • Check the status

        of your mail host.

    • NO - then...

  • Is the problem only with receiving mail?

    • NO - then your problem is outside the scope of this example.

    • YES - then...

  • Is your email account name correctly entered on your email client's configuration screens? Your account name (e.g. cher0123) is quite different from your email address (e.g.

    • NO - then enter your correct email account name.

    • YES - then...

  • Does your email account have a new or recently changed password?

    • YES - if your email client stores your email account's password, check that its configuration has been updated to use the new password.

    • NO - then...

  • Is your account over quota? You may have received an email message from IT Services informing you about this.

  • Is your mail host machine running normally? (Check the IT Services "System Status" web page.)

    • NO - wait for the host problem to be resolved.

    • YES - then...

3.4. Scenario D - Erratic Freezing, Hanging, Crashing and Bombing

Freezing, hanging, crashing and bombing are all terms that people use to describe a computer that suddenly stops working while in use. These terms are not totally consistent in how they are used but broadly speaking:

  • Freezing

    - usually describes a system that has suddenly become completely inactive whilst running. There are no error messages on the screen, the mouse pointer does not move, and pressing keys has no effect whatsoever - not even producing beeps etc.

  • Hanging

    - usually describes a less severe form of freezing. Things have ground to a halt, there are no error messages, but the machine is not completely dead. The mouse pointer may still move and, on a PC system, pressing the Ctrl/Alt/Del key combination produces a response.

  • Crashing

    - usually describes a situation where a program has terminated abnormally, often with some kind of error message. The machine may still be usable.

  • Bombing

    - the Macintosh equivalent of hanging/crashing. A message (accompanied by a picture of a bomb!) appears. Usually the system needs restarting.

Freezing is usually symptomatic of a hardware fault, or of a non-Plug-and-Play device that is internally misconfigured. If it occurs erratically, the problem may be due to a component that fails when it gets warm after the machine has been in use for a little while. If you turn the machine off and let it cool down, it may work normally for a while. Keep a log of its behaviour and how soon after switch on it misbehaves.

Hanging, crashing and bombing are generally more likely to have other causes which can be investigated further. If you suffer from these, then note whether the problem always occurs at precisely the same point, or only with certain documents, or only after having run certain other software etc.

4. Step 3 - System-specific Diagnostic Tools and Techniques

4.1. Windows 95/98 System Troubleshooting

The Windows 95/98 onscreen help system (accessed via Start->Help->Contents->Troubleshooting) has a interactive troubleshooting section covering some of the most common problems.

Chapter 35 of the Windows 95 Resource Kit, and Chapter 27 of the Windows 98 Resource Kit also give a good introduction to Windows troubleshooting. Information on these and other resources are included below in Step 4.

Some of the most common causes of Windows 95/98 problems are:

  • Insufficient resources

    - insufficient memory (RAM) or free disk space can cause some software problems. If an application runs fine on its own, or when processing small documents, but misbehaves when running at the same time as another program, or when handling large documents, then this could be your problem. Another symptom of insufficient memory, is a high level of disk activity all the time you are using the machine. The solutions are to add more RAM to your system and/or to do some disk "housekeeping" to try and free up disk space. The Resource Meter (accessed via Start->Programs->Accessories->System Tools) can be used to monitor various aspects of your system's memory usage.

  • Faults in Specific Software Modules

    - these may often be remedied by installing a relevant update or "service pack" from Microsoft or other software manufacturer.

  • General Protection Failures (GPFs)

    - occur when Windows encounters a problem it cannot handle in an orderly way. Insufficient resources and faults in software modules are common causes of GPFs.

  • Problems with Device-drivers and Configurations

    - each hardware device connected to your machine has a software device driver to control it. Device drivers are installed and configured via the appropriate Windows control panel. On "Plug-and-Play" systems, Windows will automatically and detect Plug-and-Play devices. However, with older systems or devices which are not Plug-and-Play, some manual configuration of the device may be required. Alternatively, a device-driver may have problems which can only be cured by obtaining an updated version from the manufacturer.

Windows Safe Mode If a serious Windows problem occurs, such as a badly misconfigured device, you may need to use Windows safe mode. This runs Windows in a mode where device drivers are not activated and therefore cannot misbehave. Sometimes in such situations, Windows automatically starts up in safe mode. If it doesn't, you can request this - press the <F8> key as soon as you see the "Starting Windows" message during system startup; you should be presented with the system's Boot Menu which should include at least the following options:

  • Normal
  • Logged (Bootlog.txt)
  • Safe Mode
  • Step-by-Step Confirmation
  • Command Prompt
  • Safe Mode Command Prompt Only

Choose the Safe Mode option to run Windows in safe mode. There are occasions on which you might also wish to use the Command Prompt option - this takes you to an MSDOS-type command prompt.

In safe mode, you can use the various Windows Control panels to add, remove, re-install or re-configure device drivers via the Windows Control panels. If you restart the system in its normal mode, use the Device Manager section of the System Control panel to check the status of any device.


The ScanDisk utility included with Windows 95/98 is a powerful disk-fixing utility. If Windows is closed down improperly, ScanDisk normally runs automatically. However, you can also run it by starting up your system in Command Prompt mode (see previous section) and typing the command SCANDISK at the command prompt.

4.2. Apple Macintosh System Troubleshooting

The Macintosh onscreen help system (accessed via the Troubleshooting topic on the ? or Help menus) has a interactive troubleshooting section covering some of the most common problems.

The most common errors on Macintosh systems are Finder Errors, Bus Errors, and Bombs. Common causes of these are:

  • Corrupt/outdated Application Software

    - Bombs and Finder Errors can be caused by a corrupted application program one of its associated files. This is the likely cause if these errors have started to occur only when using the same piece of software. If this happens a reinstallation of the software in question will often fix the problem. However, a good starting place BEFORE reinstalling the system is to remove any preference files for the application from the System Folder/Preferences folder. Sometimes, older versions of an application will not work with a new machine or system software version. In this case, an updated version of the application will be needed.

  • System Extension Conflicts

    - If the errors do not seem to be linked to a particular application, or occur during system start-up, then it is possible that two or more system extensions are conflicting. In version 7.5 and later of the system software, this can be tested by using the Extensions Manager Control Panel. By saving the current (non-working) set of extensions and then turning off the loading of different extensions until the problem disappears, it should be possible to deduce the extension that is causing the problem.

  • If your system does not start up correctly you can switch off all the extensions by holding down the <Shift> key during the initial startup process - you should see a message Extensions Off on the Welcome to Macintosh startup screen. If the machine starts correctly without the extensions then you can use the process above to turn on extensions selectively until the problem starts again.

If you find you are experiencing a number of errors it may be worth reinstalling your system software - but before doing so try removing the Finder Preferences file. A fresh 'clean' set of preferences will be generated on startup and this can help in resolving system problems.

Handy Keys for Troubleshooting

Here are some key combinations which may be useful when troubleshooting Macintosh Problems

  • Switching Off Extensions on Startup

    - To prevent extensions loading on startup hold down the <Shift> key while the system starts up. You should see a message "Extensions Off" as the system starts up. This can aid in troubleshooting problems caused by extension conflicts.

  • Rebuilding the Desktop

    - To rebuild the Macintosh's hidden Desktop file, hold down <Option> and <Command> keys (these are also sometimes labelled the <Alt> or the <Apple> key) while the machine goes through its startup sequence. Near the end of the startup sequence, you should eventually get a message asking you if you want to  rebuild the desktop file for the startup hard-disk (to rebuild a floppy disc desktop hold down the keys as you insert the disk). Rebuilding the Desktop can eliminate problems with corrupt icons and devices (such as CD-ROMs floppy discs etc.) not mounting correctly.

  • Zapping the P-RAM

    - To zap the P-RAM (Parameter RAM) hold down together the <Option> , <Command> , <P> and <R>keys and restart the system - release all the keys when the system restarts itself a second time. This clears the contents of the P-RAM which holds the current date/time, monitor type and other hardware / device details. If a machine is behaving erratically and software problems have been eliminated then zapping the P-RAM, forcing the system to refresh its settings may help. Note that you will need to correct the Date and Time using the Date/Time Control Panel after zapping the P-RAM. The P-RAM contents are maintained by a small battery. If your machine keeps forgetting its date/time setting, this battery may need replacing.

5. Step 4 - Finding Solutions

Once you have narrowed down the problem, you have a much better chance of finding the solution.

5.1. Vital Statistics!

Before you start seeking a solution or contacting a help desk, you should collect together some basic details about your hardware and software. Some potential solutions may only be relevant for certain types of system or software versions. The most useful information includes:

  • Computer make and model (e.g. Viglen Contender II, Mac Powerbook 520)

  • Processor type (e.g. Pentium II, Core 2 Duo)

  • Amount of memory (RAM) installed (e.g.. 1GB RAM)

  • Hard disk capacity and amount of free space (e.g. 70 GB and 20 MB)

  • Operating system version (e.g. Windows Vista Home edition, Mac OS 10.5)

  • Application version if relevant (e.g. Word 2007)

In Windows 95/98/NT most of this information may be obtained by right-clicking on the My Computer or various disk-drive icons and choosing the Properties option. Within an application, the Help/About... menu option usually includes version information.

On older PC systems, the MS-DOS utility MSD run from the command prompt displays a useful variety of system information.

On the Apple Macintosh, the About... option on the Apple menu gives basic system information. Disk size/free-space information is given when you view a disk's contents in an icon view.

You should also be able to give the precise symptoms of your problem, e.g.


"When I use the File/SaveAs option with a particular document in Word 97, the program crashes and displays the message 'GPF at location 0001234:32 in module MSFILE.DLL'. Other documents behave OK on my system, and the problem document behaves normally on other machines running Word97"

rather than

"I can't save files on my PC"

5.2. Hardware problems

  • For machines still under warranty, the supplier or manufacturer may have a telephone help-line. If they have a web-site, it may give details of UK phone numbers for getting help - see our list of hardware manufacturers' support pages.

  • If your computer has been registered with the University's Microcomputer Maintenance Scheme, then contact the service company direct to request an engineer call-out. (Note, you cannot register with this scheme if your machine is already faulty!)

  • If your machine is out of warranty and not registered on a maintenance scheme, then if a repair is needed you will probably need to use a suitable hardware service centre - the manufacturer may be able to suggest a service agent.

5.3. Software Problems

6. Step 5 - And Finally...

A very old piece of computer wisdom: If all else fails... read the manual!


Written by IT Services. Latest revision 27 March 2015