I think the first thing to try is another anti-virus scan, just in case. Use Windows Defender Offline
to do this. This is not
Windows Defender nor Microsoft Security Essentials. It is another Microsoft program designed to scan and remove viruses before Windows boots. This can get rid of more stubborn infections.
If that scan comes up clean, you should either try a Clean Reinstall
or a Repair Install
if you cannot back your files up to an external disk. A clean install is pretty much guaranteed to work but a repair install might not. However, a repair install is easier as all your documents, settings and programs will not be affected. Details of both are located in the tutorials.
If you want to go ahead and do a clean install instead of following my other advice (which is fine) be sure to follow the tutorial to do so. It shows how to do so without a Windows 7 DVD to save you buying one if you don't have one. It is also full of helpful advice on what to do afterwards to make sure you get the best result.
Hope this helps