Laptop starts up and down in an endless loop?

I have a laptop here that, when you turn it on, briefly lights up the screen (but still black) and then goes out after a few seconds. This repeats itself in an endless loop and you can't go into the BIOS / Uefi. What could be the possible causes of this problem, are there ways to identify it and possibly even repair it?

I would be very happy to receive answers.

The only thing I could think of would be to reset the BIOS to factory settings, since you would not even have to go into the BIOS for. But as with a laptop - if at all - you would have to google.

So using a jumper or CMOS battery?

Yeah, I just don't know if it's so easy with a laptop. Has also a security aspect.

Then I'll see if there's anything to be found.

As mentioned here, resetting the BIOS is an idea. Even if it sounds less like a problem with BIOS settings.

Do you remember what happened to the laptop before that? Did the laptop shut down during normal operation and then did not start up?
Have there been any falls, water damage or the like before?

Is the power cord plugged in when starting up? If so, try it without. If not, you can also try to remove all batteries and then start the laptop with a cable.

I opened the laptop and looked for the jumper or the CMOS battery, unfortunately without success. The manufacturer's maintenance document does not provide any information, and the search for information on the mainboard does not provide anything: /

Peep tones don't come either.

This is not my laptop, but I was told that it was probably used to watch series on the bed. Then he fell asleep and when he woke up the problem was there. So my first guess was maybe overheating because the fans couldn't draw air through the bedspread or anything like that.

Have already tried both, with and without a power cord.

Ah, then it may well be that the laptop has ridden off to its ancestors. It actually sounds as if it has overheated and some component has broken as a result.

That doesn't sound good. I would not say now that the laptop is forcibly over due to lack of information, but it is very possible. The best thing you can do now is remove the hard drive and save all the data.