First As your computer starts but before Windows launches, press F8, this takes you to safe mode.
Next click START then RUN and type this exactly
%SystemRoot%\system32\restore\rstrui.exe
Click next and choose a date at least a week before things started going wrong.
Follow the prompts to complete the process. PC will restart itself and should be fine.
Next use a virus scanner such as AVG(Free) to rid your self of those viruses.
Dave, March 2007