A few times in the last two weeks the sound and picture has gone off while watching one of our HWS. The green light stays on and the TV's power light stays on. I can press guide on the remote and see it. I can press cancel and see the cancel screen. The only way to get the picture and sound back is to press channel up or channel down. Selecting a show from the guide doesn't even work. Software U233. Neither the HWS nor the TV have automatic shutoff set. I have done a reboot by pulling the plug, waiting a few minutes and plugging back in. Any suggestions?