PCI-E(s) Giving "No Signal" Black Screen

Motherboard: AsRock Z75 Pro 3
Graphics Card: GeForce GTX 570 HD
Also tried: MSI RX300HM-TD128E
Power Supply: Corsair CX 750

The motherboard is new, as is the power supply. The graphics card (the GTX) isn't. I'm trying to make it work without having to reinstall 7. With the integrated graphics I can get in fine, it'll boot, I can log into Windows, etc. The problem is that it won't boot from PCI-E; all I get is the "no signal" black screen with all the lights, fans, etc. running.

If I'm running from integrated (via BIOS choice) it will notice the graphics card, and even name it correctly in Windows. It has done this for the MSI and the GeForce cards. I also tried unplugging the integrated and plugging in the MSI while it was in Windows and it continued to work, so it's not like the card isn't working at all.

I did try switching the BIOS option to PCI-E first (which it was by default, I had to switch it to get it to work in the first place) and got the "no signal" black screen. I tried another card (the MSI) to see if it was just the card, but the problems persist. I downloaded new drivers in both instances.

I should also note that it takes a while (sometimes 1-2 minutes) to shutdown.

Any help would be appreciated : ).

Just so we can rule it out, you've plugged in both PCIe power connectors to the GeForce video card, right?

Sure have / did.

Have you disabled "IGPU Multi-Monitor" in BIOS?

Huh. That seemed to do it; I hadn't bothered because it mentions XP / Vista only in the manual, but I'm not going to look a gift horse in the mouth.

Thanks very much for your help, much appreciated! I know it's not a graphics card issue, but do you have any idea why it might be taking so long to turn off?