Double check the temps though I doubt it would be overheating right from the start. Return everything to stock clocks (if you overclocked anything) and double check that your GPU is firmly seated and has the power connections it needs.
When you uninstalled the beta drivers did you run a driver sweeper or something similar to get rid of any driver fragments left over? That is also something to try.
Going to try to use a driver sweeper to fully uninstall the beta drivers, and then I'll reinstall 14.4 again. Really hope my computer's not screwed up too badly. I was just playing Bioshock on it last weekend, too.