Dell Inspiron 5675 won't work with RX 480 8GB

I got a second hand Inspiron 5675 without a CPU. I ordered a replacement ryzen 5 1600x. I replaced the stock power supply with a thermaltake smart 500 watt PSU, and replaced the 4 GB RX 570 with my 8 GB RX 480. The 480 was also used when I bought it. I had previously reflashed the BIOS on the 480 to solve driver issues. I had used this card in this computer before, and had no issues, but out of nowhere my Inspiron won't boot with the RX 480. The RX 480 works on my Dell optiplex with the old power supply from the Inspiron. If you need the specs of the optiplex I can add them later. I tested the slots with another gpu, and it boots just fine with my AMD fire pro w5100, and my Rx 570 that came with the computer. When I boot the computer with multiple gpus, I can see the RX 480 in device manager and adrenaline. I can't connect another display to the RX 480 even though the computer can see it. Is it likely that my motherboard is the problem? Or that my Rx 480 is failing?