Monitor gives no picture of the pc?

So I have a new pc and an older monitor from aldi.

wanted to check out ma bios this afternoon, but then the monitor didn't turn on. The monitor is only on when the pc is started and runs for about 10 seconds (has ne SSD). If I then switch off the d3n monitor again or switch on the monitor too early, the monitor does not recognize the pc.

Both are connected to a HDMI, the pc has only one hdmi and 2 dp connections on the gpu, the monitor has no dp connection.

I'm now aware of the fact that bios no longer works with the buttons when starting, so I wanted to start bios with restart + shift, but then the pc "turns off" and thus the monitor, which then no longer recognizes the pc. I have already checked the cable and the monitor with the old pc → worked and have already removed the gpu and plugged in via the other connection → same problem and also checked the ram and removed the jumper and the mainboard battery for the bios reset → problem still not solved, monitor does not recognize pc. I don't have a second monitor, my mom only has an old laptop and I don't have the money for a new clever monitor.

HDMI devices do not have to be "recognized". They have to work as soon as the cable is plugged in and the connection is OK.

If the "monitor" should be a smart TV, it must be switched to HDMI with the AV button.

Ah okay ^^ '

well the cable is plugged in, it is not a smart tv and the monitor says 'no signal' after switching on after a short time and goes into standby

And the monitor is set to hdmi