ASRock Z97 Pro4 won't output to GPU?

[LigTasm]

I'm working on a build for a friend, he had this board and a 4770k new in box for months now and decided to have me build him a rig.

Here is the problem, I cannot get a discrete GPU to work with either of the x16 slots. Plot twist: the slots work and detect the GPU just fine, or any other card you put into them. The machine will boot into windows with the GPU in on a black screen.

The onboard video works perfectly, with no issues. However, nothing works in the slots. Is this a board problem or a CPU problem? I tried a sound card in both slots, works fine. Tried a pci-e x4 SATA card, works fine and runs hard drives. GPUs are detected by windows, you can install the drivers and everything, but no output.

If I change the BIOS to PCI-E gen 1 or 2 like many suggest it makes no difference. I have updated to the latest BIOS.

Any ideas?

 

[LigTasm]

I figured this out in case anyone comes across it. My PSU on the test bench is an Antec HC750 that is not Haswell compliant, changing to an EVGA 750G2 fixed the problem. Apparently the compliance extends past sleep states.