So I just got a new motherboard the other day, the ASRock Extreme3 Z77, and it seems to work great, but for some reason when I try to boot the system with my GTX460 and the GTS250 for Physx, I am unable to boot past the BIOS screen and it just hangs there. With either card in either of the slots though it boots fine with no problems.
It seems like a hardware issue but I'm not entirely sure. It seems like you've got an OS on your hard drive already, so something must be preventing your computer from booting up with a dual card setup. Maybe you need to download all drivers for each of the video cards?