Sorry for the late, i have read about it only now.
I have the same matherboard and one year ago i tried to upgrade my gpu, from Radeo HD 5570 to an Rx 550, but i had your same problem.
Obviously the system with the old gpu worked perfectly, it wasn't a psu problem.
I think at 99% that it was the mobo (old bios), maybe because it has pci-e 2 but it should support the 3 standard.
If someone could help to find a bios of this mobo it would be fantastic!