Why does the picture turn black after a short while, but sometimes not?

I have the problem for some time, that when I turn on the PC he simply displays no picture when booting. So I see the connected controller that the PC already starts (fan etc I hear synonymous) so he is definitely on, but there's no picture. If I then restart it several times (by power button) then comes after many attempts a picture which usually goes away after about a minute ergo black. So the PC was properly ramped up at this time could see the desktop, but then ausm Nix is the picture then gone again. It is also no Wakelkontakt the monitor cable or something. Then after several attempts he then drives "normal" high so that the picture remains auhc. But it's annoying to feel him driving up and down for 5-10 minutes and I'm also afraid that he will not be able to do it any more soon. Also, I sometimes see on the controller that he seems not only the picture is gone, but he also reboots. (The green circle on the Xbox Controller then flashes and then becomes the player 1) which is not always. When I first had the problem it was only black once and then when I started it up everything was back to normal. But over time it got worse and worse, so I needed more tests now.
I hope I could describe the problem well, because it is not always the same and I also have not a clue how I can formulate that well.

Theoretically, it could be almost everything, I would tap on the graphics card, but a remote diagnosis is always very difficult.

Do you know when it happened?

It could also be on the controller - try it from the pc without starting the connected controller

Unfortunately, it also spins with the controller
well that's been like this for a few weeks now

Graphics card could be possible, because this is very old.

If possible, I would check, if that with another Graka (on board, separately, what is available isr is). If not, it's probably because of Graka or its drivers.

The screen gets no power, exchange power cables on the screen or check whether it is loose or is not properly in the screen

No, he gets electricity
it still shines, but the picture is black
I'm not that stupid, either

That's what I have to do before I just have to wait