How to stop cable box from nap mode

All of a sudden by cable box has gone into inactive or nap or sleep mode so what I am recording is just a screen with the Comcast pic of weather and time. I have never had this problem before. I have unplug the box and restarted it but keep happening even when I am home & have tv on after 4 hours it ask if I am still there. Why am I pay a lot for cable when your device is destroying anything I try to record when I am not home or late night?