5090 x ASRock taichi x870e lite

Hi People,

first time builder Here. Me and my dad wanted to do a PC build together but but a big Error occured which lets out heads explode. First our Specs:

ryzen 9 7950x

GigaByte GeForce RTX 5090 Windforce OC

MSI GeForce RTX 5090 Ventus 3X OC

(yep, 2 GPUs)

128gb RAM

ASRock taichi x870e lite

Seasonic Prime px 1600

As you could guess, we spend a lot of Money on These parts and saved Up a long time. Everything works and fits. but the GPUs are Not doing anything. Not even the Fans move a little bit at start. Already tried changing the places, Trying only one on wach PCIe but nothing. tried the original seasonic cable and the ones that got delivered with the GPUs. Tried almost every Setting in the BIOS that i could find and Had to ask AI (honestly AI didnt Help me much). So now me and my dad are very sad because we think the Money Just vanished and we dont know what To do.

I Hope someone had the Same Problem as me and Has the Magic solution. (excuse my english, im from Germany)