Sudden restart loop then black screen

Hello.

Yesterday I was using my MacBook just fine, connected to the power, when it suddenly restarted: I was in Bootcamp and initially thought it was a Windows 10 issue, but then the Mac partition wouldn't boot and kept restarting; at one point it got stuck on a boot chime loop which wouldn't go past a white screen, then nothing. Now it's stuck on a black screen, no chime, fixed white power sleep light.

My situation:

• Two SSDs with one replacing the optical drive slot
• Non Apple RAM upgrade by Crucial replaced in 2016
• Non Apple battery replaced about a year or so ago
• Original power cord cable, never replaced

What I tried to figure out the problem:

• The usual key combinations to reset NVRAM (useless since it won't get to the chime sound part) and SMC
• I removed my SSDs (white screen with ? symbol), I also checked them with another computer and they're fine
• I removed the Windows SSD and put the optical drive back in to see if I could hear it start, and it does start
• I disconnected the iSight camera
• I reseated the RAM, tried to boot with only one in, then switched
• I removed the RAM and the Mac obviously didn't start without that, but it beeped and I read somewhere on here that's probably a good thing?
• I tried booting holding down the Eject key, the Shift key, D/option+D, Cmd+R, etc. and the only thing I noticed is that the sleep light blinked for a few seconds then stayed fixed again
• I put the original Apple RAM back in and if the Mac is connected to the power and has the battery disconnected, once every 20 to 30 tries the computer goes to a white screen and then actually boots. It stays on for a while, then suddenly turns off for no apparent reason. However, I only managed to make this happen twice in about 6 or so hours, so I'm not sure it's a viable conclusion…
• If I just try to turn it on, the power sleep light blinks 5 times then stays stuck on white.

Now, what could be the issue that makes this all possible? I never had any kind of hardware problems with this computer so I'm really confused and kinda hoping it's not a logic board failure.

How can I know for certain whether it's that or a RAM issue? Considering even the original RAM isn't spared from the black screen (though it does turn on with that after numerous tries)? Would a logic board failure still make the Mac occasionally boot and work?

I really hope someone here can shed some light on my situation. I care a lot about this computer and would like to see it working again. Thank you for your time.

UPDATE 16/03/2021: Replacing the logic board fixed the problem.