I'm about to lose my mind over this. I have a machine I built summer of 2013 which originally included one GTX 780. I recently purchased a second card (exact part number), and inserted it in the 8x PCI-E slot (the original card being in the 16x slot). The new card did not register at all aside from the fan spinning up and the cards lights working (it did not show up in device manager / nvidia control panel, etc). I then removed the original card, put the new card in the 16x slot and everything worked fine on its own so the new card wasn't defective or anything. But when I connected the old card back into the 8x slot the now the old card was not recognized. No matter what I did, the second card would not register when both were connected, this is with and without the bridge.
I was under the impression that if there is no card in the 16x slot then a single card should work in the 8x slot - so I gave this a shot. Neither card would give me video when used independently out of the 8x slot except for 1 -2 times, which led me to believe that there was an issue with the 8x slot (I temporarily though it might have been a seating issue although everything seemed to indicate otherwise, but just to be safe I used an old invidia card with no clearance issues and when seated perfectly still no video out). I tried the usual driver wiping and reinstalling, updated the BIOS version to F8, etc etc. Multiple people told me I probably had a faulty motherboard so rather than wait for an RMA, I just bought a new Z87x-UD3H and tried again. Same exact issue. Something I had originally overlooked was connecting power to the ATX4P connector on the board, still no change.
So in summary, I have 2 GTX 780s that when both connected will not register the card on the 8x slot regardless of which card is in which slot. The problem is persistent on two different Z87X-UD3H motherboards. Does anyone have any ideas that may help before I toss myself over a bridge?
