Can you be more specific about what virus(s) you think you have? Have you checked for spyware and other nasties?
is an amazing program for spyware removal. It sounds like a windows update may have caused you some dirver grief. After making sure the machine is clean (do the scans in safe mode, or pop the hard drive out and scan it from another computer), if it is still acting up, attempt a system restore (assuming you have XP or Vista), (start->accessories->system tools->system restore). And restore to a point in time when you weren't having any troubles (you won't lose any data).
If that doesn't work, do a repair using a windows xp or vista cd. You will need to re-enter your license code, but it is NOT a reformat.
Here is a link with detailed instructions on how to properly do a repair if it comes to that point.