I'm running Vista Home premium

Question

I'm running Vista Home premium on an HP Box with a Nvidia GeoForce 8400 GS video card. Worked great for about 7 months and now I keep losing the video with a "no signal" error on the screen after a few minutes of having it work. When I reboot it typically comes back with terrible resolution and color indicating that the driver status is"Windows has stopped this device because it has reported problems. (code 43)"I've ran every Windows update and auto find driver change which fixes it after reboot for about 5 minutes. I've also tried the driver pack from NVidia's site with the same results. Help?????