Whoa! This happened to me some years ago. I had Windows but the virus wouldn't let it run. Let's try this first:
Try getting rid of the virus in Safe Mode. Windows will not be loaded and hopefully your AV program will catch any self-executable files.
Safe Mode is:
Turn your PC on or Restart. As soon as you see the black and white screen, press and hold the F8 key. Continue holding until you see a black and white menu. Safe Mode is F3 or F5.
Click Start, Programs, run your AV program.
When it is finished, Restart.
You will probably find your icons messed up. Just drag them back into place.
Is Windows o.k. now?
If not, try a repair -- you didn't say what version Windows you are working with, so take your pick.
http://search.yahoo.com/search?ei=utf-8&fr=slv8-&p=windows%20repair%20tool
If this fails, I think you will have to go for a complete format and reinstall.