It is probably infected with a virus, since restore points (backups created by Windows) are either corrupted or deleted by virus or a malware.
The best way will be to format your system and re-install your Windows with a clean CD. Do remember to take backups of all your data. Another important thing before formating; you should have all the drivers (display, motherboard, networking, printers and scanners) in hand.
A solution by Gianiji.com
Gianiji.com
March 2008
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