Somethings wrong...Help..Motherboard,Virus or what?

Recently I attempted to upgrade my cpu in a Compaq Presario 7585.I made the exchange and found that my P.C. would not work properly(no video).So I put the old cpu back and rebooted,everything was fine,at least I thought.
At some point either before the cpu swap,my pc acquired the infamous W32.spybot.worm.My pc started acting strange,and naturally I thought it was maybe soemthing I may have done while exchanging the cpu.My 2005 PC-illin,Micro Trends suite did not detect the infection.Actually it had two other viruses..Norton found them.
After that I could not get Windows 2K pro to install properly.It would always hang at the point you type in the codes.It would just flash like crazy like multiple windows were trying to access at the same time.Now if I pressed the Control key it would stop then I could type the codes.Now if I continued this installation,at the point you would logon you would get this ''conflict'' again.I could not cease until I press the control key again.And this would always happen at the logon window unless I hold down the control key during the loading of windows.Then it would load up seemingly okay.But it never would work properly,always buggy.
Then I tried installing Win XP.That went a little better as far as installation goes.Never working like it should.It does all kinds of crazy stuff,freezes,hangs.Opens multiple windows at any given time.Help me,please help me....Like in ''The Fly''!
Now could the virus still have an effect after reformatting,repartioning,even ''wiping'' the hard drive before installing XP.Should I get a new HD or could my motherboard be damaged or what?
I also tried a new hard drive and the same problem occured during the installation as described above.
Help, a wanna be Nerd!