Thanks, I'll have to take a look at my bios later when I'm back at my rig. This guy's video is fairly basic. Leaves most things at default/auto values. If memory serves, the pcie x16 section in the bios is under PEG. I think I tried every option - auto/gen1-3. Will go back and check later. I hope the slot is ok...
![Undecided](https://bitcointalk.org/Smileys/default/undecided.gif)
Last resort would be to actually unplug all other cards and try with only one card in X16 slot.
First you can try to turn of rig and try to plug in /plug out riser few times in that slot, there may be some contact problem due to dust or oxidation.
Yeah, looks like I'll have to try the slot solo with the card directly in it next. I retried all combinations of auto/gen1-3 for all pci options. The slot is red (error) on the detection screen when I plug any riser in.