I suspect there are still some old driver segments left behind from the original drivers. Did you run Driver Cleaner Pro while in Safe Mode? If not, try uninstalling your drivers using System, Hardware, Device Manager, and the video card (Display Adapter) uninstall. Then reboot into Safe Mode, run DC Pro, empty everything from the recycle bin, then re-boot. When Window starts and tries to install new drivers, stop it and direct it to your new drivers.
Somebody else had the same problem (same video card) and found it was caused by upgrading the BIOS. Here is their commentary: "I did some looking into what was going on and the problem was that the bios was upgraded. We contacted Asus and they told us that should not be done unless there was a conflicts with the one that he had. So I back dated the bios to the one that he should of had and he got 10778 (ed, from about 6000) on the bench mark." Maybe something there if you recently upgraded the BIOS...
Work any better?
Noel