On one of our TVs (we have 4) we are unable to receive a picture or sound. When we turn on the the TV and the cable box, we are able to get the menu to come up. When we swicth to a channel, we get the menu bar at the bottom identifying program, the picture may come on for a brief second, then nothing. We have double checked all connections. Is this a problem with the signal strength coming into the house? We are not having any issues with our other TVs.
Try swapping locations with a known good unit. This will check activation and the cable box.
Also, sometimes some TV's just don't like the resolution they're getting from the cable box. Try rebooting the cable box while it's connnected to the TV (and the TV's on...) to see if it might not 'decide' on a different resolution.