I don't know if anyone thinks this is relevant, but i had the same problem, i really twigged on it when i upgraded to my GTX 760 and had the same problem as my old 550Ti... i didn't really think much of it at first with the 550 because it was old, so i just overclocked until the card drivers crashed and reset, then it worked fine til restart. But i've noticed that the Newest NVIDIA drivers are what's doing it, i uninstalled them with Driver Cleaner Pro... then installed the version of the drivers from the disk that came with my Card... and it's working fine, i've posted a thread on the NVIDIA forums, just waiting on a response now...