It would be a good idea to run a virus scan without booting up the possibly infected OS.
You can do that with a bootable CD/Virus scanner. The AVG rescue is a good option.
AVG Rescue CD: http://www.avg.com/us-en/226386
You can also try running the Malicious Software Removal Tool from Microsoft. Type MRT into the Start menu search bar.
(always run the system in Safe Mode while you do scans).