Well, is your vid card being properly cooled?? Is the heatsink hot... I mean hot to the touch.
Does the heatsink have a fan??
Is the air temp inside of the case hot, moving hot air across the heatsink does not help much.
As for the only weird issues I had, I had to flash the bios for the video card before I could get it to work properly with the Nvidia drivers.
G4 MX440 Leadtek