You boot your computer, and your stomach lurches. You are faced with the ominous “blue screen of death”. This could mean anything from a hard disk crash, memory failure, virus attack, or some fatal error in Windows. And if you have not backed up your data you may see your work of immense value gone forever.

We often forget the basic tenets of computing. So lets re-jig your memory this week and go back to basics.

The principal reason why Windows crashes is hardware conflict. Each hardware device communicates through an IRQ (Interrupt ReQuest) — special numbered channels used by devices to get the processor’s attention. For example, a printer usually connects internally on IRQ 7. The keyboard usually uses IRQ 1 and the floppy disk drive IRQ 6. Each device will try to hog a single IRQ for itself.

If there are a number of devices, or if they are not installed properly, two of them may end up sharing the same IRQ number. When you try to use both devices at the same time, the computer can crash. To check if your computer has a hardware conflict go to Start-Settings-Control Panel-System-Device Manager. If a device has a problem a yellow ‘!’ appears next to its description in the Device Manager. Highlight Computer (in the Device Manager) and press Properties to see the IRQ numbers used by your computer. If the IRQ number appears twice, two devices may be using it. You can remove the problem device and reinstall it.

Sometimes you get a message saying Fatal Exception Error, which indicates a serious hardware problem. Sometimes it may mean a part is damaged and will need replacing. This may be due to RAM (random-access memory) problems. A fatal error caused by RAM might be due to a mismatch of chips. For example, mixing 70-nanosecond (70ns) RAM with 60ns RAM will usually force the computer to run the entire RAM at the slower speed. The machine will crash if the RAM is overworked.

One way around this is to enter the BIOS settings and increase the wait state of the RAM to make it more stable. Modern RAM chips are either parity (ECC) or non-parity (non-ECC). You should not to mix the two types, as this can cause trouble. If you get an EMM386 error message, it may be due to free memory problems linked to old DOS-based programs.

A common BIOS error concerns the CAS latency. This refers to the RAM. Older EDO (extended data out) RAM has a CAS latency of 3. Newer SDRAM has a CAS latency of 2. Setting the wrong figure can cause the RAM to lock up and freeze the computer’s display. You can press F2 to get into the BIOS settings in the first few seconds of a boot up. BIOS access methods vary from F2 to F12 to pressing the Del key on boot up. Set the IRQ numbers to Auto in the BIOS. This will allow Windows to allocate the IRQ numbers (make sure the BIOS setting for Plug and Play OS is switched to ‘yes’ to allow Windows to do this.).

CAS is short for Column Address Strobe. Latency refers to the time that you are waiting to get what you need.

It is also a good idea to defrag your hard disk every week. Go to Start-Programs-Accessories-System Tools-Disk Defragmenter.

Some lockups and screen freezes caused by hard disk problems can be solved by reducing the read ahead optimisation. To adjust, go to Start-Settings-Control Panel-System-Performance-File System-Hard Disk.

Hard disks will crash if they are too full so free up space every few months by deleting the contents of the Temporary Internet Files folder on C drive. Every week, empty the Recycle Bin and scan your disk drives for errors or bad sectors. Go to Start-Programs-Accessories-System Tools-Scandisk. You can also assign the Task Scheduler to perform this at night when the computer is not in use.

Finally, your screen can freeze because of viruses so make sure your computer is virus protected. We will deal with this again next week.

Send your computer-related problems to askdoss@abpmail.com with bits&bytes as the subject line