It’s good that we know the problem is with the video card. We have some computers in the office using 770s and they don’t have any freezing. Therefore, I’d recommend updating your drivers; it’s possible that you just have an outdated driver for your 770 and that’s the issue. If that doesn’t fix it, then there may be a hardware defect with the card, which means you’d need to send it back to its manufacturer (if it’s still under warranty).