i guess its possible its a knackered card, it happens. try the drivers off www.tweakforce.com
they sometimes fix problems too, not always but hey worth a try at this point, u might also need to reinstall windows, this could be the problem, cant really think of much else.
oh and ive also read somepeople having problems with pre overclocked cards, perhaps uneed to use a tool like rivatuner and underclock the card back to default settings. then see if it makes a difference.