You've probably got Sasser.
To stop the timer: On the taskbar at the bottom of your screen, click Start, and then click Run.
Type: cmd and then click OK.
At the command prompt, type: shutdown.exe -a and then press ENTER
Go here:
http://www.microsoft.com/security/incident/sasser.mspx
and here:
http://securityresponse.symantec.com/avcenter/ven....removal.tool.html