Yeah, that would be my advice normally too but in this case reinstall your computer.
Does your computer say, the administrator want you to shut down the PC bla bla bla save documents the computer will reboot in variable amount of seconds...
If so thats the blaster virus!
When your in your clean installation install programs like:
Sygate Personal Firewall
Nortan Antivirus 2005
Adaware
Spybot