Hello and sorry you're having problems.
By far the most common cause of this problem, is a glitch in the cable box processing.
Please follow the steps below:
1) Shut the TV off, and then disconnect the cable/SAT box from power.
2) If using an HDMI cable, disconnect and reconnect the HDMI cable on both ends when the cable box is unplugged from power (make sure it's secure on both ends).
3) Plug the cable box back into power, and once it's rebooted, turn the TV on and attempt to watch a program.
If this does not work, then please tell me how specifically the DTV box is connected to the TV (using what type of cabling).
Feel free to reply back if you need more help, or want to reply back with more details. It does not cost you anything more to reply back once you've rated. Please do rate me positively (at least 3 STARS) and I will continue with you until this is sorted. The positive rating ensures I am credited for my work.