elvis123456789,
The nVidia graphics chipsets in the 8xxx series have known issues that cause them to eventually deteriorate. And since (to my knowledge) none of them are separate from the motherboards, only option is replacement.
I knew this when I was given a laptop a while back. It had no issues at the time other than software, but it's a ticking time bomb. Either one day it will burn up and die on me, or maybe I'll get lucky? From what I've read about the issue, I think it's more just a matter of time.
In your case, time has run out, it seems. Time to go hunting for a new motherboard or new laptop. If you want to try to keep the same laptop, you could try searching to see if they made a model with a different video chipset. On mine (Dell XPS M1530), some had the nvidia graphics, and some had intel. The intel based ones had no such issues. 'Course, they also can't exactly play just any game you want, either.... but if you have an 8400 it won't be as big a loss as from my 8600GT.