Try removing the booster the Comcast guy installed. If that works, put it back in between the splitter and the cable box.
Otherwise, describe how things are hooked up in detail (eg "cable drop to splitter input, one splitter output to TiVo input ... ").
Otherwise, describe how things are hooked up in detail (eg "cable drop to splitter input, one splitter output to TiVo input ... ").