No live view and Info screen

Help, I have a d 5100 and when I plug a HDMI cable
into the camera and to a 7 inch monitor, the camera
goes dark, no live view or info on the camera screen just on
the monitor. I have another 5100 that works fine, the
7 inch monitor and screen on camera work fine
together. What the ???

That is probably correct. Many times an external monitor will shut down the monitor on the camera.

I have another 5100 that works fine the
7 inch monitor and screen on camera works fine
together. What the ???