Could be a million and one reasons for this, but in summary it usually means that either your Windows installation is corrupted or that you have a hardware problem, particularly with your hard drive.
Eliminate the drive problem first.
Start -> Programs -> Acessories -> System Tools -> ScanDisk
Choose to scan your hard drive, make sure the 'Thorough' option is selected, and click on the 'Advanced' button and make sure you have it set to 'Display Summary'.
If the check reports lots of 'Bad Sectors', replace your hard drive.
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Grandad
Offline 3,826 posts
since Mar 2004