Hello, I'm Shahid. Sorry to hear that you're having trouble with this but I'll do my best to help.
- We need to isolate the issue first, can you try another video source into HDMI input of TV to see if TV shows picture?Thanks.
OK, lets try easy thing first.
- Have you tried to unplug TV and cable box power cords from wall outlet for 10 minutes to reset, replug back in, let cable box reboot that may take several minutes and check?If not yet, please try it now and reply back with the result and if problem resolved then a positive rating to answer would be highly appreciated.
Switching Off by pressing power button on TV or its remote may not help, you would need to disconnect power leads from wall socket for 10 minutes to get them reset, replug back in and turn them ON and check.