1x to 16x powered risers not working.

[animentis]

I have an MSI z77A-GD65 board a 1600w PSU, some sapphire 7950's and some 1x to 16x Powered Risers. 

The cards work fine when plugged into the board, but the card connected to the riser doesn't appear to be recognized by the system.  (actually it might have once but it still didn't do anything)

Is there any particular reason that jumps out as to why this would be?

I should note that I haven't tried to plug all of the cards in via the powered risers... I have simply plugged 3 cards directly into the board and followed up with a 4th on a 1x slot to test - not sure if that would make a difference.

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[Cryptocables]

Could be a couple reasons

1) You have a bad riser
2) If you are plugging in a 1-16x riser into a 16x PCI slot, you may need to short the slot depending on your motherboard in order to get it to function
3) Try a different port on the board if you have one available if its none of the above to see if its a connection issue