Hmm so a rig stopped mining after being 8+ months stable.

Now all of a sudden it has completely lost the ability to detect a GPU via riser.

Plug directly >>> all GPU work
Plug via riser (any slot, any GPU, any riser) >>> no lights, no fan, no nothing. Yes I tried many many risers from spares etc.

I stripped the rig down to 1 GPU with the same results;
Directly >>> fine
Riser >>> nothing at all. Not even a LED!!!