How to connect mac mini to 2560x1080 monitor?

Question

Mac Mini

I have a mac mini 2011, the monitor is connected via displayport to mini displayport, with a resolution of 2560x1080. Through HDMI, it only supports 1080. Everything worked well, I left the computer for the night, when I turned it on in the morning, there was no image. When the computer is turned on, the monitor works. Shows loading up to half and turns off. Reinstalling the OS didn't help.
If both cables are connected, then the computer sees, as it were, 2 monitors. One with a resolution of 2560 × 1080, and this resolution is active. But about the fact it is still 1080
But if you remove HDMI, then the computer stops seeing both monitors.
What could be the problem?

Answer 1

Perhaps in the mini displayport - displayport cable, did you try to change it?

Answer 2

The cable works because I wrote that the beginning of the download was shown on the monitor.
After 2 days and a reinstalled OS, it turned out that you need to turn off and turn on the monitor with the cable connected and it all worked.