Hi there,
I can give the "solution".
The risers I have seem to be really instable. After plenty of different tries, I get the GPU starting on Riser with the PCIe x16 port.

So, no config problem or else... Just bad hardware quality I think.

I spent hours on this :-/

Thanks for your feedback, i tested with 2 different Risers.

And still blocking the launch.
I tested to start with riser WITHOUT GPU and it's starting.
I tested with not alimented GPU on the riser and it's starting.

It only blocks when I have the wullriser with GPU installed.

Thanks for the tip of bios flashing, i did not try that.

Hi,

I am stuck in the RIG construction.
When I plus the GPU directly on motherboard, the system boot perfectly.
When I use a riser, the system does not boot (i can't even access to the bios). The fans of the GPU are correctly working.

I spend time checking every seting in the bios but do not find anything obvious.

MB : MPG Z390
riser : https://images-na.ssl-images-amazon.com/images/I/81A0nbQZyuL._AC_SL1200_.jpg
GPU : RTX 3070

I try to change the GPU and change the riser (all the components) without any change.

If you have any idea on how I can use the 4 PCIe slots on the MB, I am stuck :-/

I just command other Riser (another type) but 3 weeks delivery.

Ben