Bizarre issue: ASUS PRIME B550M-A WIFI II, Ryzen 7 5700X

[OVERKILL]

My son has an Alienware socket AM4 system w/Ryzen 7 5700X in it that he wanted to migrate to a new Corsair case, so he bought a case, but hadn't realized that the Alienware board had a proprietary back panel, so that took us board shopping. Unfortunately, the case he bought limited him to MicroATX.

Now, the Alienware water cooling setup uses an Intel bolt pattern (as does their board) so he had to order another kit, got a Thermalright setup for it that supports AM4.

Ordered him the ASUS PRIME B550M-A WIFI II AM4 board, put it all together, no POST.

Tried a minimal config, still nothing.

Tried:

-4x different video cards (and two we know worked in the Alienware board)

-2x different sets of RAM, with a single stick tried in every slot

-Re-seated the CPU

-Cleared the CMOS, pulled the battery



Took it all back apart, tested it all in the Alienware board, it worked.



So, I contacted ASUS through their Chat, they recommended I RMA the board. While I was waiting, I figured I'd order another as an advanced replacement, which arrived today.

EXACT same symptoms with the replacement board.

I cracked open a new PSU (ASUS ROG 850W) and tried that "just in case", still nothing.

The board powers on, video card fan spins, but USB never initializes. Some quick googling led me to similar symptoms with ancient BIOS versions and incompatible CPU's, but this CPU has been supported since 0303 and both these boards shipped with 3607.

I've now ordered another CPU to test with, a Ryzen 5 5600XT, just to confirm the board works (which I assume it will), but I have a very hard time with the idea I received two defective boards that exhibit the exact same symptoms.

So, the CPU works, but not in this board, even though it is supposed to.