Laptop keeps going to black-screen, repair centre couldn't diagnose.

My Inspiron laptop (i7, RTX 3050) suddenly went to black screen while I was using it. I had to perform a force shutdown but now it won't restart (no signs of life/power).

I've had this problem a few weeks ago and took it to a repair centre to run diagnostics. They disconnected and reconnected the battery and it worked perfectly for them (were unable to reproduce the issue). I took it home, same issue happened again, took it back, and again they restarted it by disconnecting the battery. 

They ran checks on battery and all the major components and Dell's diagnostics came back as all-clear. Eventually they had to hand it back because they couldn't find the issue. The laptop worked perfectly fine for about 3 weeks since then, but a few minutes ago it black-screened again and I can't restart it.

Biometrics stopped working on the device shortly before the first black-screen event, which makes me think it could possibly be an issue with the power button. The biometrics worked for about 30 minutes after the first repair (and their diagnostics showed it as working fine), although has remained inoperable since.

Is this a common issue with these laptops? Are there any potential solutions?

Edit: I have tried force-shutdown (15 seconds). Battery was fully charged and laptop was plugged in when all events happened (power cable's light is illuminated). In all cases system was under light load (just a single browser tab open). No visible damage to the laptop or knocks that might explain internal damage. BIOS was updated to newest version by the repair centre. I have tried restarting unplugged and plugged in, laptop shows no sign of life.

Edit2: Okay, in an even stranger turn-of-events, the laptop turned itself back on without any input from me. After I wrote this message I closed the screen and went next door for 10 minutes or so, when I came back I noticed the battery light was illuminated again, and on opening the screen the laptop automatically started up again (I have the setting disabled in BIOS for startup with open screen). I didn't press the power button. Laptop appears to be functioning perfectly now, although I expect it's only a matter of hours/days until the issue repeats itself. Any help would be greatly appreciated.

And it's not a case of my pressing the power button and not waiting long enough for it to start, I pressed the power button and waited the entire duration of time it took to make an account on Dell and write this forum post, and on previous occasions I've tried completely draining the battery before starting up again. This is some very odd behaviour.