Hey man,
I had a similar problem with gigabyte 9800gtx+ nvidia card on same
GA-MA785GMT-UD2H motherboard,nine was that certain games started ok but then became corrupt eventually hangin the pc,by chance I came across sonething that my card is overclocked by default,si i reduced the memory speed fromm 1000hz to 750 and its never happened since.
Worth a try.
I use HUD utility that came with card,downloadable from gigabyte.
good luck