[Troubleshooting] SLI/Potential Motherboard Issue

Hey guys, I posted a build on here a few months ago. Everything went swimmingly, until today. I used some Christmas money to buy a second graphics card to take advantage of SLI, but have run into a problem. With the second card in, I no longer make it through BIOS. The BIOS loads and acts completely normal, then it says "Loading Operating System..." like it always does, but whereas the next screen would usually say "Starting Windows" as the OS loads, I'm simply kicked back to the beginning of the BIOS. An endless BIOS loop.

The graphics cards are EVGA GTX 560 Ti's, and both work fine by themselves, so the new card isn't dead. My power supply is a Corsair TX850, so there should be no issue there. So I assume it's the motherboard. I have a Gigabyte Z68 (GA-Z68A-D3H-B3, Rev 1.0) with the latest BIOS (F11). From everything I've read online, there's no reason it shouldn't be working. From what I can tell, the Z68 has a PCIx16 slot, and a second PCIx8 slot, so that if you run SLI both slots run at x8/x8. I've read that this isn't a problem as the GTX 560 can run x8/x8 with practically no decrease in performance.

So, I ask of you, any ideas? Should I look into a beefier motherboard? Or is there someone here who can help me, or at least direct me to where I can be helped? Thanks a bunch guys.