so you think the board is just broken? normally there is no such problem? or may there be another reason ?

Hi Guys,
dunno if this is the right place or not, but im desperatly looking for help by now :/
Wanted to get my mining rig going the last days, but my Asrock z97 Extreme 4 cannot detect more than 2 of my 5 r9 390 Gpus. Im using powered risers for all of them. At first, the 1x PCIe slots didnt even recognize the cards at all, but after shorting the A1 to B17 Pins on the 1x Slots, at least i got 2 of my cards running at the same time. Every time i try a third, the third card is powered when starting the Windows 10, and the fans are rotating, but my system doenst see the third gpu. MSI afterburner and claymoreminer dont see the third card either, its not working. i already tried switching cards and slots and stuff in every possible way, there are always just running 2 of them, so no changing slots or cards option here. i figured out that the pci slots may need to be turned to GEN1 / 2 / 3 or something, i already tried that by changing it, but im not quite sure which is the right setting, considering i have 2 options in bios whcih i could chance (Pci slot 2 and 5 or something like that). do i miss something here? do i need to change anything else i didnt think of yet?
forgot to mention, i got more than enough power, considering i bought 2 PSUs so all 5 cards with an consumption of 300w each (i know its a lot) would work. my bigger psu has 1200w, so 3 cards and system are no problem, so thats not the solution either!
any help would be apprectiated, i hope i didnt forget any important detail
greetz and thx!

Hi Guys,
dunno if this is the right place or not, but im desperatly looking for help by now :/
Wanted to get my mining rig going the last days, but my Asrock z97 Extreme 4 cannot detect more than 2 of my 5 r9 390 Gpus. Im using powered risers for all of them. At first, the 1x PCIe slots didnt even recognize the cards at all, but after shorting the A1 to B17 Pins on the 1x Slots, at least i got 2 of my cards running at the same time. Every time i try a third, the third card is powered when starting the Windows 10, and the fans are rotating, but my system doenst see the third gpu. MSI afterburner and claymoreminer dont see the third card either, its not working. i already tried switching cards and slots and stuff in every possible way, there are always just running 2 of them, so no changing slots or cards option here. i figured out that the pci slots may need to be turned to GEN1 / 2 / 3 or something, i already tried that by changing it, but im not quite sure which is the right setting, considering i have 2 options in bios whcih i could chance (Pci slot 2 and 5 or something like that). do i miss something here? do i need to change anything else i didnt think of yet?
forgot to mention, i got more than enough power, considering i bought 2 PSUs so all 5 cards with an consumption of 300w each (i know its a lot) would work. my bigger psu has 1200w, so 3 cards and system are no problem, so thats not the solution either!
any help would be apprectiated, i hope i didnt forget any important detail
greetz and thx!