Downgrade monitor issue, how to resolve?

[GaryWayneSmith]

I set this unit us using my Samsung 4K TV and it's working fine. But the 4K is used for something else. I picked up a 24" 1920x1080 monitor and it detects it on boot up but then goes to black screen, never again showing anything. If I switch to the 4K, it's there, back to the other monitor, nothing. It's almost like the OS isn't changing the video to the proper resolution.

Is there an easy way to fix this?

 

[Fishrrman]

Which Mini do you have?
What year was it made?
What version of the OS?
What ports are on the back of the 4k display?
What kind of cable connection are you using?
To which port are you connected on the Mini?