Fallout 3/New Vegas issue

So i just bought an Asus GTX 560, and installed it into my system. Installed the drivers, ran Fallout 3, runs smoothly. Reboot, try to run Fallout 3 again, loads game menu, loads loading screen, black screens with an error that a problem is preventing this program from running. From here I looked up the latest drivers and downloaded them. I had to manually uninstall the old drivers, reinstall the latest drivers, and bam, it works again. Then I reboot, and try to play again, and it does the black screen when game play should start.

System:
MOBO: ASUS Maximus III Formula
CPU: Core i5 at 2.67GHz
RAM: 8GB DDR3-1600
NEW GPU: ASUS GTX 560
OLD GPUS: SLI GTX+ 9800 (X2)
PSU: 850W Corsair.

ALSO: Runs Crysis on HIGH settings with no problems. So i think its a specific matter of Fallout 3/New Vegas,

I'm not sure if its hardware or software or what, but any help in the matter would be greatly appreciated.
Thanks