Update: I realize now when I watch Live TV on the problem Tivo the screen is blank. If I change channels with the Tivo it tells me the channel and the program content but nothing shows on the screen. I thought I was watching live TV before but I was doing it on the other Tivo hooked up at the same location and the straight cable feed coming though the VCR. My guess at this point is that it is not the Tivo at all. But it's also not the cable feed since my other Tivo is recording right now. And all the wires and cords are completely inaccessible to both pets and humans so I doubt that the cats or the cat sitter could have done anything. I'm still at a loss.