Fellas,

I  have an Asus prime Z270-a and it's supposed to run up to 8gpu, though I can't even get the 4th to work.

I have 3 GTX 1070 and 1 R9 390 to run on there. the r9 390 isn't showing up in device manager.  I've configured all my PCI-e links according to everyone video I've seen on the board, but the 4th card just isn't showing up.  This isn't my first build, though it's only my 3rd and my first time on Asus.

Yes, the bios is updated
Yes, I've tried 3 different Risers, though the first two are known to work.
Yes, I'm only plugging the risers card into PCI-E 1x slots.
Yes, the card works when plugged into the board with no other cards.

Thank you.

I cannot install AMD drivers as no device is recognized.