I just got my gigabyte vega 56. and I went to install it on my 9370fx with a gigabyte 990FXA ud5 mobo with the FC bios. and when i tried to boot, it would turn on the radeon logo, gpu tach, and fan all turn on but i get nothing from the display, HDMI or display port. my amd r9 270X works just fine using the same power cables 6/8 pin, direct from my PSU , and the same PCIe slot on the mobo. I have an 850W power supply so it should have enough power to boot.. i messed around in my bios and enabled both eufi and BIOS bootable items, i also disabled quickboot. but still nothing. im going to go to my local PC store and see if i can borrow a newer intel or ryzen mobo to see if its not just a DOA card.. i hope not.. but we all know how things get shipped.. and i bet HBM cant handle being dropped kicked too many times.
I got the GPU tested and it works fine on a z170 board. I'm going to assume its my motherboard BIOS. It probably does not recognise the GPU