Have you tried a different cable, and the simplest output on offer? (ie, VGa, if not, dvi, then hdmi/dp). Have you tried different monitor ports?
Everything suggests that it's that or a problem with your internal hw. I looked up the board and it doesn't seem it should have any video connections, and your gpu indeed des not require subsidiary power.
Try the cables, and if not buy a gpu at a store w/ a lenient returns policy to test if it is your gpu that's a problem.
Also, what's the clock/timings on your ram? Your board lists different compatibilities there based on the cpu series you've used.
I know this may sound tedious, but please humour me. It's important to try and isolate the cause, and ideally it's something cheap like a bad...