Black screen on boot with GPU plugged in

[Djinni]

Hello,

I have a problem with my machine which is causing some unusual behaviour.

Specification:
CASE: Fractal Design Define R4
PSU: Fractal Design Newton 800W
CPU: Intel i7 2600k
Cooler: Thermaltake Frio
RAM: 12GB G.Skill Ripjaws-X
MB: ASUS P8Z68 V-PRO
SSD: Samsung 840 Evo 256Gb
HDD: 2x 3TB WD Red, 4x 4TB WD Red, 2x 1TB Samsung SpinPoint F3
GPU: Asus GTX 760
VDU(s): Samsung 2233RZ, LG IPS236V-PN, Samsung 46 F6320

Symptoms:
Black screen on power on, followed by blinking cursor.
Issue persists through GPU reseat,
Issue further persists through GPU reseat in another PCIe slot
BOOT_DEVICE_LED on motherboard is lit while 760 and 960 plugged in (and powered)
PCIe slot with these cards appears to power down to allow system to continue to boot when display not connected to them.

Troubleshooting:
GPU removed and 2 displays powered by on-board graphics appears to resolve.
GPU replaced with a EVGA SSC GTX 960 ACX 2.0, has not resolved problem.
GPU replaced with a GT 610, issue appears to be resolved.
Display connected to motherboard output with GTX 760 and GTX 960 installed (seperately). Discrete GPU not seen by Operating System.

Can anyone help me with some analysis please?

[Denpepe]

Could be the PSU went bad and can't deliver enough juice anymore?

[Djinni]

Could be the PSU went bad and can't deliver enough juice anymore?

Thought about that, but its a 1yr old 800W Fractal Design Newton PSU and the average power draw is around 300W

[Djinni]

Ok, so done some additional testing.

Plugged 2 computers into each other so that the PSU from the other was powering the motherboard + GPU of the other, alternated hardware between both boards + PSUs and the problem stayed with the motherboard.

[Vash The Stampede]

Try download Mint 17.2 and burn the ISO through USB or DVD. Boot off that and see if you get a working desktop. Cinnamon UI is 3D accelerated and if a live boot works then it's OS related. Otherwise your problem seems to be the motherboard.