Second GPU in Crossfire Setup Not Detected

[The_O_King]

Hi there, I've been a longtime LTT fan/forum lurker, but just made an account to see if you guys could help me with a problem! I have been having some problems with a PC upgrade that I am trying to setup. Here are the specs:

CPU: i5 2500k

Mobo: ASUS P8Z68-V

RAM: 4x2GB Crucial Ballistix

GPU: 2x ASUS STRIX R9 390

PSU: Corsair TX850M 850W PSU

 

So here's the issue: When plugging in one GPU into the PCIEx16 slot on the motherboard, the board doesn't seem to detect it, and instead outputs via the iGPU (and does this for all the PCIEx16 slots on the motherboard) and POSTS fine, booting into windows (No discrete GPU detected in Device Manager either). HOWEVER, when plugging in both GPUs into the top two PCIEx16 slots, I get video output from the GPU in the top PCIEx16 slot, and that GPU is also detected by Windows, however the second GPU is not recognized by Windows at all. I have tried switching the cards and they both work in the top slot, so neither of the cards are dead for sure. I have also updated the BIOS to the latest version just to see if that was the issue, no dice.

One strange thing is that with this motherboard, it can either run in PCIE 2.0 16x with one GPU or PCIE 2.0 8x8x with the two GPUs installed, and when I have the two GPUs installed, the one that is detected is running at PCIE 2.0 8x speed according to Radeon Crimson (which means that the mobo is detecting the second card in some way maybe?). So it seems to dislike running the full 16x PCIE lanes. I use to run a single GTX 560ti no problem, but now not even that is working (it gives me the same symptoms described above).

I am wondering if this has something to do with PCIE lanes? But this board is designed to run a crossfire setup in 8x8x mode?

Thanks in advanced for anyone's help!