I'm using the ASRock X870E Nova WiFi with a 9800X3D, and I'm upgrading my 3080 Gaming X Trio, which still works great. I'm using my 2 month old Corsair Rm1000e PSU.
I inserted my 5090 Vanguard and I don't ever see the fans spin or any lights. I don't see the card in BIOS or windows. It seems like it latched in the PCIE 1 slot, but I've removed a heatsink and a shroud that covers some m2 slots near the GPU to be sure it's not obstructing the GPU.
I've also tried forcing PCIe Gen 4 to be used, clearing CMOS, 3 different cables to power the 5090: 2x8 pin to 12V-2x6 included with the PSU, a brand new (from Corsair) 2x8 pin to 12V-2x6, and the 4x8 pin to 12V-2V6 adapter included with the GPU.
I'm going to test a vertical mount and PCIe Gen 5 riser cable later tonight to maybe rule out whether or not the card is obstructed when inserting it into the PCIE 1 slot.
I'd appreciate any other suggestions.