If you have a copy of windows it may just be easier to backup any important documents/files and reinstall windows, that way you know 100% that you dont have any virus/spyware and the machine should run perfectly, if the hard drive still spins up after a clean install of windows you know its the hard drive on its way out.

Installing windows might sound too long winded for some, but ive done it so many times its like eating a hot dinner to me