Question PC doesn't work with graphics cards

[danielhetherington12]

I have a pretty big issue where the PC doesn't show any image on the screen with a pcie x16 gpu.
I've tried it with an x8 gpu in the x16 slot and it works perfectly.
I've tried it with a Gtx 770 and the pc turns on and stays on but with no display. I then tried it with an HD 7970 and it just stays in a constant restart loop. All connectors are connected and I have tried it with 2 different high quality 600w power supplies and 2 different motherboards. I really have no clue what the issue is. The slot on both is pcie 16x 2.0.

 

[tennis2]

GTX770 is PCIe x16.

Is this a prebuilt machine? Perhaps Dell/HP/Lenovo/etc?

 

[danielhetherington12]

Nope its a custom built system. I tried it with a gt 710, an 8x card and it worked fine with display