One day you were working fine with Windows XP and the next day when you switch your PC on you get errors saying a file is missing or corrupt. The boot error will look something like:

WINDOWS COULD NOT START BECAUSE THE FOLLOWING FILE IS MISSING OR CORRUPT:
\WINDOWS\SYSTEM32\CONFIG\SYSTEM

This error occurs because the System registry hive is either corrupt or deleted. As the System registry hive contains the configuration information for the system to boot.

You will need your Windows CD to resolve this as you will need to boot from it. So dig it out and dust it off before you continue.

You will also need to make sure you can boot from the CD. If you can't boot from a CD then read the page Booting from CD in which you will get rough instructions on how to change this.

OK you have now booted up from the CD and you have the option to run the Recovery Console. Once you are at the command prompt type in chkdsk /R /F (remember spaces). This may take some time to run, so go and make a drink and watch your favorite TV programme.

Once this has run remove the CD from your machine and reboot.