Well, it's not your PSU, I doubt your Phenom II X3 720 is bottlenecking it, especially overclocked...
Have you tried these steps:
1. Uninstalling nVidia GeForce GTX 470 graphics drivers.
2. Shut down, then bootup into Safe Mode.
3. Run Driver Sweeper (download it first before running into safe mode) and remove all leftover files.
4. Install newest nVidia drivers.
No, but i did that and that doesn't work.