XP System Restore won't restore??

Hi Guy's, for some reason my Windows XP System Restore won't restore I have the settings at 12% & it is showing the bold restore points on the calander but after completing a restore (or trying to!) I get a message saying "the restore was not completed & no changes have been made to your computer - please choose another restore point & try again" - It just does the same with all the restore points ?

I've tried turning restore off & reboot but it just keeps storing the restore points & does the same thing?
Any ideas why this is hapening?

Thanks, Sandy.

Have you tried in safe mode? Sometimes a virus or spyware can cause this problem.

Here's a link
to the microsoft site.