UPDATE: I fixed it!! It was the PSU.
So I just built my first PC in like 20 years. Everything was going fine, I was installing Windows and got to the network setup step and my wifi was having trouble staying connected. I figured it was because I hadn't set up drivers yet, so I thought whatever, no problem, I'll just move it by my router and plug in an ethernet cable.
So I powered off and moved it, and...dead. Nothing is happening when I hit the power button. No fans, no lights, nothing. I've made sure no cables got jiggled loose or anything. Maybe I shorted something somewhere on the motherboard? I can't see anything without fully disassembling and having to rebuild it. I really don't want to do that, but I guess I'll have to unless I'm missing something obvious. I'll test the PSU tomorrow but I doubt it's that, these are all brand new parts.
Any ideas?
Specs:
AMD 7800X3D
ASRock B650E PG Riptide WiFi
Sapphire Nitro+ Radeon RX 7800 XT
2 x 16GB Crucial DDR5 RAM
Seasonic GX-850 PSU
If you have (or can borrow) another working psu and working moba, swap them with the ones for your new ps. Your psu with the other moba, and your moba with the other psu. That will tell you which component(s) are the problem.