If it is a Virus you need to clean up the HDD/s by running a wiping program on it/them.
A reinstall of Windows only over writes the actual Windows Directory and even a Format which can be disabled by a Virus if the writer know what it is that they are doing will only write to every third sector leaving 2 sectors intact and allowing the infection to reemerge latter.
But it honestly sounds as if the Video Card if you have one has gone bad and if you have a M'Board with On-board Graphic it may very well be your RAM. Have you added any recently?
If you have it may be the wrong type and be causing timing issues with the existing RAM, but no matter what I would remove the Video Card/ Memory {if it is an On Board Video and re seat them. A good clean out inside the case will certainly do no harm either. If the problem persists after reseating the Video Card or RAM I would be trying a different Video Card that suits your M'Board.
Just one thing to be aware of some AMD M'Boards do have Known Issues with some Video Cards and just do not work properly while these are mostly confined to the ATI type Video Cards it is worth remembering if you are going to replace the existing Video Card and if you have On Board Video you can either replace all of the RAM or fit PCI Video Card as you'll be unlikely to have any PCIE Slots you'll need a standard PCI Video Card.
Try running some diagnostics with the Ultimate Boot CD available from here
http://www.ultimatebootcd.com/
Col
