3rd PC build, very strange issue. I'm out of tricks. Long read.

[OilMagnate]

Because the power button itself could be faulty, or the front panel board itself. It's just another thing that could go wrong.

But it looks like you found your answer. Was the MOBO brand new? Did it look like it was a return? Amazon sometimes sells things that are advertised as new, but are returns. Of course, brand new boards can be faulty too.
Doesn't matter, return it asap. I had good luck with Gigabyte boards.

Gotcha. Yes, the MOBO was positively new when I bought it. MSI doesn't seal their boxes but I'm an expert with identifying items that have been tampered with. I actually solved a case for GameStop last year when they had a rash of Samsung SSDs being returned in empty boxes. I had to solve the mystery because I received one, and when I claimed I received the box empty I can only imagine what they were thinking. It was a bad packaging design on Samsung's part - no window to see the SSD from the outside, and the tamper-proof label could be bypassed via another seal that wasn't tamper-proof.

I purchased the board in April of 2022, so unfortunately it is RMA only. But so far the process has been incredibly easy.

 

[OilMagnate]

I was actually looking at the MSI Z790 Tomahawk but got the ASUS Strix Z790-E. ASUS motherboards are pretty good but their RMA process is probably one of the worst I've ever come across; I've had to RMA an ASUS 2080 before (for the bad Micron vRAM batch) and that was the worst RMA experience. The best advice I can give for an RMA process for computer hardware is to list all the troubleshooting steps you've done that eliminates the possibility of other hardware causing the problem. That tends to cut down on all the "follow these steps first" and straight to "here's a shipping label."

They are great boards. I now own two Z790 Tomahawks and one Z690 Tomahawk. Love the blackout look and love that they make things simple for those not as experienced (BIOS Flash drive included and ready to go). No stupid shark fins either. It takes maybe 10-20 minutes to get them fully operational from the first power-on. The Asus board took me 5 hours and a lot of forehead pain from beating my head against the wall, and still had issues. Sugar-coating it the nicest way possible, it was one of the most user UNfriendly things I've ever come across.