Since it sounds like it is a really recent problem, you may want to restore your computer to an earlier point in time. See this article for info on how to do this. Note any programs you have installed since the restore point will be removed.
http://support.microsoft.com/kb/936212/
Jeff
Windows Outreach Team
I have a Sony Viao laptop. (VGNCR307E)
When I copy information from my document folder to send via email, as soon as I click paste a message appears tha windows is restarting.
Window keep restarting everytime. I haven't had to problem until this weekend.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic