This happened to me with a few of the 6970 bios i'd tried with my 6950.
I followed this guide to correct it:Link
I had intrernal graphics and a bios switch on my Graphics card. So i would switch the bios on my GPU, then under my MOBO BIOS changes the primary video device to the Internal GPU, then switch the BIOS back on my video card, then boot to my USB and flash the original BIOS. Then change the primary display device back to the 6950.
Edit: Which video card (brand, etc) do you have? Adding your signature rig to your profile will make it easier for us to assist.Edited by GreenieGriz - 3/11/12 at 6:05pm