---- OK so after a couple of hours of barking up the wrong tree, the issue is that the Motherboard on this PC does not support UEFI, and the RX 570 evidently needs it. It didn't even cross my mind to check if the Mobo had it.
I bought a Dell Vostro 260 (i5 2400) for $60 and tried to put in a working RX 570 GPU and... it doesn't work in it. I updated the Bios to the latest version (MS-A10), reseated the RAM, the GPU all the cables. I've basically done everything found through google search.
The GPU works on my other computers, just not this latest one. HELP!
PS. I switched out the Power supply for a Thermaltake 500w 80plus and replaced the (2x2) 4GB RAM with a single chip 8GB RAM.
---- OK so after a couple of hours of barking up the wrong tree, the issue is that the Motherboard on this PC does not support UEFI, and the RX 570 evidently needs it. It didn't even cross my mind to check if the Mobo had it.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic