Question Cannot even boot to BIOS after motherboard/CPU/RAM replacement

[Vee.S]

All I have to work with are the EZ debug lights which are on for CPU and Dram and the fact that the fans and RGB from the Corsair lightning hub and from the board all work while on. I have checked for installation damage and everything is like new that I can see (CPU, RAM, MB pins, board itself, etc.). Let me get the specs out of the way first:

Specs that haven't changed:

GPU: Galax RTX 2070 SUPER

PSU: Corsair RM850

Cooler: Corsair H150i Elite Capellix

Case: Corsair iCUE 5000T

OS Drive: Samsung 980 1TB


New parts replaced:

CPU: i9-9900K -> Ryzen 9 7900X

Motherboard: MSI MPG Z390 Gaming Plus -> MSI X670-P Pro Wifi

RAM: 2x Corsair DDR4 16GB 3200MHz -> 2x Corsair DDR5 16GB 6400MHz

I have tried it with and without the graphics card, including running the monitor from either. I have tried singular sticks of ram and in different slots, as well as no ram. I've removed all hard-drives, double checked my power cables to the CPU and MB, and tried reinstalling the CPU. At first the fans would stay at maximum when I booted, but now they calm down after a few seconds. I have found the manuals for the motherboard to be beyond useless for anything beyond basic instructions and specs, and from what I've seen in forums that's pretty standard for similar boards to mine. I really want to keep going on testing before sending it back, as if they tell me that it all looks fine then I'll never know what went wrong when I personally installed it.

Any help with ideas or tests will be beyond appreciated, I'm devestated that even a bare-bones installation could go so wrong and I don't have any spare compatible components to do things that way.

 

[Vee.S]

Notes using a meter at the power socket - When the PC is "running" without a GPU it uses about 40W of power, only a few watts higher during the first few seconds of booting. Not sure if that says the CPU is quietly alive, or if this board and the cooling alone explains that.