Try taking out the second video card. Since you seem to have older hardware, this may require physical changing of jumpers etc to disable SLI mode (or, it could be that these were set wrong in the first place, as this can sometimes happen and do funny things to the video subsystem in lieu of just refusing to boot).

"I built the system specifically for gaming"

Yes, unfortunately, intent doesn't count for much as far as that argument goes. Otherwise, I could whip out the 6 year old hardware I have around collecting dust and multibox on that instead of my Q6600.