How to stop cable box from shutting off by itself

i've seen this question posted by other users here but none of them have gotten an answer. After a while a warning comes on asking if we are still watching and if you don't respond by hitting Select the cable box shuts off.. What is causing this and how do I stop it from happening? It happens on all channels at all times, not just on channel 3 or four. I have already checked the sleep timers and all other timers and no timers are set on. Please look into this and tell me how to correct this.