I had the same problem not too long ago. Suddenly had no audio or video. Luckily I had left the component cables hanging next to the DVR and reconnected them. Audio and video was restored. I left it like this for a couple of days but refused to believe that the HDMI cable had gone bad as it was fairly new. So I reconnected the HDMI cable and sure enough audio and video was restored. It's been fine ever since then. I think communication gets lost between the box and TV.