When you say it is "ridden with virus/spyware" do you mean it is full (riddled) with these or that you have got rid of most of the virus infections.
Have you tried to run HiJackthis. It will give a read out that the mega tech brains on here can read and maybe point you in the right direction before you resort to reformatting.
http://www.spychecker.com/program/hijackthis.html