I have a rig with an AMD 7970 and an AMD 7950.
Both work in any PCI-E with the old flat clable risers, but if i try to use PCI-E usb 3.0 risers they don't boot unless i'm using the PCI-E 16X slots.
both cables have presence pins shorted, tried in bios to change to PCI-e GEN 1, 2, 3, auto.
Anyone know something about it? is it the board? looks like im going to have to check what's the difference from flat cable and usb.