Common problems
Console has no picture
A console that powers on with no picture usually has a damaged HDMI port, often from the cable being yanked.
Signs
Console turns on and you can hear it, but the TV says no signal; picture flickers; the HDMI cable feels loose.
Try this first
Try a different HDMI cable and TV input. Look in the port for bent pins with a flashlight.
What we do
We replace the HDMI port, clean the board, and test with several TVs.