See if you can get a replacement for the card from the manufacturer. If that fixes your problem, then that meant your current one is faulty or something went wrong with it.
Hopefully that will fix your problem but if that does not, then it points to either corrupt drivers, conflicting drivers, or some interfering software. Did you uninstall previous graphics drivers before you installed the current ones for your graphics card?
http://www.geforce.com/drivers
just curious but what game(s) are you trying to play?