Question PC boots bit doesn‘t show anything on screen, how do I identify the problem

Nov 23, 2019
Recently, I‘ve run into some problems (crashes, running slow, etc) with my PC, though most were solved after either a restart or, in the case of recent boot looping, reseating ram. It started about a month ago with my pc running far too slow (struggling with browsing on chrome, game fps ~2x too low), which was then, after it turned out to be caused by software, resolved by resetting windows.
About two and a half weeks ago, I had my first crash while running a demanding game. It ran as good as it always did and suddenly, my fans got very noisy, followed by my screen being covered in weird white symbols (all over the place), distorted colors and black areas and eventually my pc restarted. After that, it ran normally again.

I thought this was the end of it, yet about a week later, after I shook my table pretty hard (PC was on the table), it crashed again (This time without the weird screen) and boot looped whenever I tried to start it. I soon fixed the issue by, as mentioned, reseating my ram.

A few days later, while browsing on chrome, the crash with the weird screen happened again, followed by boot looping. I tried reseating ram yet the boot looping continued. After leaving the PC alone for about a day, it worked again (?)

The crashing with the weird imagery on the monitor continued to occur far too frequently and eventually, the PC wouldn‘t boot after one of the crashes.

I pressed the power button, fans ramped up, leds started glowing and the bios screen popped up. After loading for a bit, it went to black screen and my monitor showed „no signal“

I read somewhere that I should reseat everything, did that, and now I‘m here, after pressing the power button, fans turn, lights are on yet the monitor stays black, not even a bios screen showed.

So far, I‘ve tried to get an image on screen by using another, working gpu, made sure the monitor was working with a console and reseated everything I could while, of course, restarting a lot of times.

I‘m at the end of my wits here, what can and should I do? If you need more info, please ask!
Thanks in advance.