Its entirely possible you do not have enough power.
You have a quad rail PSU, kind of like 4 different PSUs in one box, with a max rating of 18A per 12v rail.
Now, this is all well and good, but the issue comes with balancing the rails....
One will almost certainly be reserved for the CPU and motherboard. The other 3 will be split between PCIe connectors and drives.
It could be that you are unlucky and your PCIe connector is on the same rail as all your drives, and that one rail is overloaded.
It could be that you have blown one 12v rail by overloading it, and that one is no longer powering the card.
I'd suggest trying the other PCIe connectors. You have two 6+2pin connectors and two 6pin connectors, so just juggle them around.
Failing that, buy a decent single rail PSU such as a PC Power and Cooling one. My 1kW PSU has a single 72A rail