Laptop does not recognize its own monitor?

As already stated in the title, the screen of the monitor is no longer valid. If you connect a second screen, the PC can be used, but only in the sealed mode and only via VGA cable. In normal mode or with HDMI cable, it crashes directly. If you take the safe mode, you can then see in the screen selection menu that the screen on the laptop is not displayed, so not found. Since the system is still running under Windows 7, I tried to play Windows 10 using a bootable USB flash drive, but that does not work either. Does anyone know what this could be all about and what you can still try?

The same thing happened to me with a MacBook Pro, about ten years ago.
Diagnostics was broken, the flat cable from the graphics to the screen.

At that time, the cable was not extra to get, the entire screen had to be replaced. It had been stinking - but it was worth it for the supermachine.
For the money, I would have two PCs… I do not like it. I've already got it, is Spitzgras.

Can you go to the BIOS with the external monitor? And is that perhaps synonymous with HDMI? Or is it synonymous only with VGA?

…

Otherwise, if this is a normal notebook and only the internal cable is defective you can swap this. Material costs probably around 20 euro.

If the graphics chip is defective then a repair is usually not worthwhile.

Yes, you can go via VGA cable into the BIOS. But that does not do much either, because even if you then put the bootable USB stick in the first place, the system crashes directly without secure mode.

Well, then hopefully you have only a broken internal monitor cable.

It is best to open the notebook and disconnect the cable.

Then start the system via external monitor, if it goes via HDMI.

If that does not work then probably your chip has suffered.

Unfortunately, you have not written which laptop model you have exactly.

In case of problems with display, display cable, display control the notebook should work normally.

In safe mode, uninstall all video drivers. If so he goes up in normal mode (to external monitor), it is due to graphics. Graphics chip exchange costs around 100 euro.

Thanks for the tip with the graphics driver, now he actually drives up again in normal mode. Now all I have to do is get the screen up and running again…

Then it is unfortunately due to graphics, even that can't solve. Please do not try the stupid methods you find on the net (in the oven, with Heißluftön oä.), So a proper repair can be impossible later.