Couple of things.
a ) If you leave the game in it's frozen state for a while, will it "recover" ? I've noticed this for a while now, the recovery will be done by the drivers if it can. Cause ? Personal investigation leads me to think it's a hdcp problem between monitor and card. Particularly due to extended monitor cables, poor hdcp handshaking between the two devices, all enhanced by an oc, imo. HDCP issues can show themselves when your monitor appears to go blank for no reason, then suddenly come back. If there's an age difference between monitor and graphic card, I think it's more prone.
b ) When you ctrl-alt-del, launch task manager and look for "sppsvc.exe" - if it's there close it. I've not come to the bottom of why this thing comes up, but it's part of the Microsoft Software Protection Platform Service. I did think it was users using illegally installed windows - however, I've seen it in legal ones too. Bench testers should particularly take note of this process as you can often find you're running tests and for some unknown reason you get lower results than you did before, even after applying an overclock. You close it, and the tests run ok again. I've advised people about this before and had no feedback. That an letting windows settle down from boot for 5 mins before running benches are vital for true figures.
.. if none of these seem to apply, go with the usual the guys above suggest, and re doing drivers etc etc etc