Its more than likely your board. I have heard of some particular gigabyte models that will not run Kepler in the x16 slot, I actually had to refund a buyer who I sold a GTX 670 for with the exact same problem, his AMD card worked fine in the x16 slot on his gigabyte Z68 board but the 670 would not boot unless it was in the x8 slot. No fix that I know of or was able to find, but I did find several people having the same issue with gigabyte boards only. BIOS updates also did not help.
Here are some info from the guy I sold it to:
Gigabyte GA-Z68A-D3H-B3 Socket 1155/Intel Z68/DDR3/ATI CrossFireX & nVidia SLI/SATA3&USB3.0/A&GbE/ATX Motherboard
Edited by Scorpion49 - 11/8/12 at 11:17pm
Well, it works in my second slot (8x), but not in my first. Makes no sense. DLing drivers now, and then I will retry first slot. I will keep you posted. Thanks for the quick responses...