PC does not start Windows?

I have a problem. Today I gambled on my PS4 while my PC was running on another HDMI due to Discord. (I have a very small TV that I use as a monitor). I wanted to switch to the HDMI on the PC briefly, but I got a black screen. I then disconnected the HDMI cable from the PC and turned it on again and restarted it with a long press of the power button after it still gave no picture. When it came back on, the BIOS opened and when I tried to close it, it went back on. It's been like this the whole time, I've tried a lot, e.g. Changing the boot order or calling the boot manager. Regardless of which hard drive I choose to boot, a screen always pops up with: "reboot and select proper boot device". Has Windows disappeared somehow? I have no idea what happened there, I'm not very familiar with computers and have never been in the BIOS or have changed anything. I have a gaming PC with an MSI B450m Pro VDH max motherboard, 16 GB Ram and a GTX 1660 super and Windows 10.

If the PC switches on but Windows no longer starts, there's usually a software error.

To fix the problem, boot from your Windows DVD or any other disk from which you installed your operating system. You will find detailed instructions on how to make the corresponding settings in the BIOS in https://praxistipps.chip.de/...ehts_10145.

(I got it from the website chip)