Nvidia graphics card temperature

Redownload the graphical drivers from the NVidia Website. If that does not work, try ventilating the system a bit more. Check and make sure that the graphics card is seated correctly in the motherboard. Check and make sure that the GPU is receiving enough power from the CPU (make sure the CPU can handle that kind of power output) If all else fails, call NVidia and complain and make them replace it  

I had the same problem about a year ago. First i tried the above, then i replaced it and the PSU... that worked. But try the above first, because its cheaper