H97 Anniversary with RX480 and RX470 RIG Problem

Hello,

I have build a RIG unsing H97 Anniversary MB with 1 RX480 and 3 RX470 RIG, fist of all I have update the bios of MB isert RX480 on X16 PCIe slot but I was never able to boot, I have try also with all other RX470 with the same result.
I have change the MB for a new one but I get the same problem, do you know why x16 PCIe slot doesnt work on RX cards ? There are some particula BIOS settings ?

Next step was boot the RIG using internal IGP and 1 RX480 GPU on x1 PCIe slot and riser card, this works and I was able to boot my Windows 10 OS and install the Radeon latest driver, so I start to insert the second GPU RX470 with riser and I get a driver crash and I was never be able to have this card working I have try to change all possible PCIe slot with same crash every time.

I have try also using linux Ubuntu, same problem on x16 PCIe slot that doesn't boot and same problem using 2 o more GPU the sistem crash.

What can be the problem ?

Maybe the riser card ?

I have use this riser with B85 Annuversary MB and HD7970 for some months with no problem !

Thanks

Fabrizio