Try this process to reset the TV to factory default condition. (A trick I learned by trial and error while dealing with this type of problem with various digital TVs.)
1. Unplug the TV from the power source. Keep it unplugged for about 30 minutes.
2. After 30 minutes, and while the TV is still unplugged, press and hold the TV's Power button for about 10 seconds. Then release the Power button.
3. Plug the TV set back in. Make sure you've got a good input signal from your cable source.
4. Press and release the TV's Power button. It should turn on normally and start seeking an input signal. You may have to go to the Settings menu and re-program the tuner by doing an auto-search (or auto-scan or auto-program, whatever the appropriate command is for your set). It should then search for and program the tuner with all active TV channels. Make sure you selected "cable" and not "air" (over the air broadcast).
Note: If the TV set does not power up within 5 - 10 seconds of pressing and releasing the Power button in step 4, then press and hold the Power button until the TV powers up or 10 seconds, which occurs first. (You might have to repeat steps 1 - 4 above.)
Many years experience as a master comm-electronics technician; experienced in audio-visual equipment installation, setup, and troubleshooting.