To troubleshoot your Smart TV displaying a black box on the screen, you should follow these steps:

1. Check the HDMI connection and ensure it is properly plugged in and firmly seated.
2. Unplug and re-power the Smart TV from the wall outlet for 1 minute.
3. Check to ensure the cables and connections all the way to the source device are working properly.
4. Ensure the TV and source device are both on and the TV is set to the correct HDMI input.