Unplug and re plug the USB lead from the screen to the monitor or whatever the lead is, if you have multiple connection options on the graphics card, try a different one.
Update the graphics card driver, from the manufactures website.
Is it an lcd monitor, if it is it might be a backlight problem, when it happens again shine a light on the screen and see if you can see an image.
https://www.techwalla.com/articles/signs-of-a-dying-lcd-monitor
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