Diagnosis
The TV is on the wrong input source. This is the most common setup hiccup, especially with multiple devices.
How to Fix It
Grab the remote and press the Input button. A menu will pop up on screen. Cycle through the options (like HDMI 1, HDMI 2, ANT/CABLE) using the directional pad. The correct one will be the one your cable box, game console, or streaming stick is physically plugged into on the back of the TV. Press OK to select it.
If That Didn't Work
The HDMI cable itself might be faulty or not fully seated. Unplug the HDMI cable from both the TV and your device, then firmly reconnect it. Try a different HDMI port on the TV if you have one free.
Heads Up
If you're using an external device like a soundbar via HDMI ARC (usually HDMI 2), make sure that device is powered on before turning on the TV, or the TV might not detect it properly.