[Help] PC doesn't boot properly

I recently RMAd my ASRock AB350M PRO4 motherboard because it started freezing after a few months of use. The new one arrived, installed everything on it (the same stuff that I used with the old board), and it failed to start properly.
First, there was no signal, the fans kept running for ~15-20 seconds, then restarted, repeat. After I messed around with it a bit and realized I didn't push the RAM down correctly, it kept running without restarting, but still no signal. Today, weirdly, after I reseated the ram again, it started restart-looping again.
Later I checked the CPU for bent pins (none), and reseated it, and I messed around with the ram again, but put it back into it's correct slot finally. This time though, the system didn't keep restarting, but the fans were revving up and down (not completely), and still no display...

Things I tried so far:
- clear cmos
- tried 2 speakers, no beeps (so system doesn't even get to POST, it seems like)
- putting ram in each slot
- unplugging 8 pin extra cpu power cable > IT RUNS WITHOUT FANS REVVING UP AND DOWN, but still no display
- unplugging GPU and HDD, SSD
- no lights on motherboard

I was thinking of sending back the MB again, but I'm afraid I messed up something and I might just mess it up again, or just missed something entirely, and the mb works. What else should I try?

(remember that this exact same setup worked with another one of this type of MB)

Specs:
ASRock AB350M PRO4 mb
GTX 1060 6gb gpu
Ryzen 5 1600x cpu
1x8 RAM
Cooler Master Elite Power 600W (RS600-ACABM4-WB)