Asus Crosshair V

Im helping a friend toubleshoot his computer. I brought over my computer to help him determine if any of his parts are defective.

His specs:
AMD FX 8120
Asus ROG Crosshair V Formula
GTX 660ti
1TB Western Digital Hard Drive
2 monitors connected with dvi-vga adapters

My specs:
i7-2600k
Gigabyte z77x-ud5h
GTX 670
1tb Seagate hdd


The problem that we are having is that when we installed his new motherboard (the asus one), it would not post with the 600ti. This is before we were even able to get into the BIOS. I put my 670 in there and it came up fine. We installed a fresh copy of windows without any problems. To make sure that his card wasn't dead, we put it in my computer, which was also able to boot and run games without any problems.

We have determined that none of the parts we have are defective. My card (670) works fine in both machines, but the 660ti only works in mine. For now we have traded cards because of the small hit to performance I would take vs him not having a gaming machine. Could this possibly be a compatibility issue? The Crosshair V Formula motherboard only supports PCI 2.0 so would that be a problem? That wouldn't make sense because I am able to run the 670 just fine.

If you have any information regarding this issue please help. I will be monitoring this thread closely.