I use Ubuntu 18.04. I try to connect TV by HDMI cable to my PC, but nothing is showing. And I access from the recovery mode (because I have some problems withe the normal access like the figure). When I try to access from the normal boot the screen is displaying normally, but when I access from the recovery mode nothing is showing at all.
MY PC: Dell
I solved my black screen problem by following the instructions in this answer. Now when I connect the TV with an HDMI cable, the external TV screen shows only the desktop background without the Launcher or Panel.