When I turn on 1 of my tv’s a blue banner shows up that says no video
use your TV's remote to change HDMI input to the name assigned to your set top box.
It is also possible for an HDMI cable to fail because of electrical fluctuations (storm or other power problems). If your have more than one HDMI cable, you can exchange them to see if problem resolves. Also; older generations of HDMI cables do not work for higher resolutions of video (1440p and above).