I have just received several of these cables and seem to be running into a problem not described anywhere else here.

If I have a card plugged into an adapted x1 ->x16 cable (plugging the extender into an x16 slot) the computer refuses to boot at all.  Using a combination of sapphire 5850s and 5870s on a Crosshair IV Formula motherboard.  This happens even if I am only plugging in one of the cards that works when plugged straight into the motherboard, so I am confident it isn't any sort of ATX power issue.  I have tried with, and without, the pins shorted as shown in many of the diagrams here.

I appreciate any help or insight anyone here may be able to offer.

Thank you.