Step 1 - Boot into safe mode
Boot the computer into Safe Mode with Networking. (When you boot up, after the manufacturers splash screen, tap F8 a few times until the Advanced Boot Options menu appears. With your arrow keys and the enter key, select Safe Mode with Networking.) The desktop background will be black. This is normal.
Step 2 - Try running Norton's Power Eraser tool.
You can download it for free from here:
http://security.symantec.com/nbrt/npe.asp?lcid=1033
You could also try Kapersky's virus removal tool:
http://www.kaspersky.com/antivirus-removal-tool?form=1