Recently Comcast sent out an update to some of their HD boxes (not X1 or the older, silver models – see photo) that has a power save feature. If you have a Motorola DCX3400 series (3412, 3416, etc) box, you have received this update and you may have experienced your box shutting itself off.
If you have no picture or see an error message, simply go to your box and hit the power button. Once your cable box is turned on again, press the Menu key, then go to the Menu option, select Setup, then you’ll see Power Save. Select that and turn power save off.