I wanted to merge two of my dual card rigs into a single rig.

The one with the asrock mobo perfectly works with 2x 7850 gpus, but wont even boot with 1  VTX3D 7870 tahiti le card (with or without the new risers). The 7870s perfectly worked in my ASUS P5K motherboard, but it has only 3 slots unfortunately.

I just can't understand how is it possible that a 1 month old gpu does not work in my ASROCK 870 EXTREME 3 R2 motherboard. I have the most recent bios flashed on it.

Anyone experienced something similiar?