The blue screen of death David. You might get lucky and chase it down, but Windows degrades over time until the only real solution (assuming it is software related - and it usually is) is to reinstall Windows. A real PIA.

I strongly suggest when you get your new pc, that you buy Norton Ghost (or a similar product) and make a drive image once you get it set up how you like it. Even better, a library of images over time. It saves a lot of time if you ever have to re-install Windows and all your apps.