So last week I bought a HD7950 MSI twin frozer retail together with my:
Intel I5 3750k stock clocks
4GB Kingston DDR3 ram (memtest passed all)
Asrock H61M-GS mobo
Antec EarthWatts 650W
I plugged it in correctly, and the card has enough power. Booted up and installed drivers fine on Windows 7 first. But once I got into a game, it would crash withing 5 minutes, saying that the display driver has stopped working and has recovered. This happened with every single game and it would clock itself back to 500mhz. I formatted and installed Windows 8 and tried normal and beta drivers, both same problem. My temporary solution was to downclock it to 700mhz, where it has never crashed on yet, but I'm losing performance this way. When I disable turbo/overdrive, it still crashes.