1) Clear CMOS, and place a single DRAM module in the slot furthest from the CPU
2) Try without the discrete GPU inserted again. Connect the omintor to the onboard DVI/HDMI out.
3) See if the board will POST.
If none of that helps, maybe describe how you had the system setup when it was working - was it overclocked in any way? Any recent changes? Did you update UEFI?