I originally posted this in the graphics card section, but I believe this is more of a motherboard issue as I have no problems with the cards. Here's the problem:
I just recently installed a new EVGA NVIDIA GTX 460 SE and I put my old GTS 250 into the second slot for PhysX. Every time I start my computer, it restarts about 4-6 times before I have to press F2 to load the BIOS defaults....every time. I have the necessary power for both of the cards as I have a 1100W PSU. I don't know what I need to do to stop it.
Weird thing is, if I plug the DVI connector into the GTS 250, I can see the screen while it boots up, but if it's plugged into my main GPU, it doesn't show anything until the windows splash screen comes up.
This is the motherboard
It's an MSI NF980-G65, also listed as NVIDIA nForce 980a SLI.
I didn't realize anyone could mix two different graphics cards in sli mode and get a stable system. That's new to me. If you can't fix the problem, I would try each card separately and choose one; sell the other one or use it for a spare.