Lost screen on Panasonic 55 inch with Mac mini
Try resetting your NVRAM (formerly PRAM).

Resetting NVRAM


Shut down your Mac. 
Locate the following keys on the keyboard: Command (⌘), Option, P,
and R. 
Turn on your Mac. 
Press and hold the Command-Option-P-R keys immediately after you
hear the startup sound. Hold these keys until the computer restarts
and you hear the startup sound for a second time.
Release the keys.


After resetting NVRAM, you may need to reconfigure settings for speaker volume, screen resolution, startup disk selection, and time zone information.