No Media Device Message - DirecTV

Sick to death of AT&T! It seems like (actually, it IS) every month, I have to reboot something. Unplug this, reboot that, etc. Why am I not getting paid to be an AT&T repair person? NOW I have a "No Media Device" message on one of three televisions. Anyone have a clue what this is or what to do? I have to waste MORE time troubleshooting AT&T's services than I really care to. Would appreciate any help anyone can offer about this No Media Device Message on my television. As soon as my contract is up (not soon enough for me), I am outta here. I thought Time Warner was bad for these kinds of issues. NOT HAPPY!
Thank you.

This question, "No Media Device Message," is about DirecTV channels, programming, equipment, and sports.