I know this sounds crazy, but bare with me. Last Christmas I bought my parents a Dish's DTVpal DVR. Almost right away they started having problems with reboots and such. They live 25 miles away, so I don't get there often to diagnose, but after installing firmware updates, many of their problems went away. I'm not sure if they are on the newest firmware right now though.
OK, my father says that the remote works fine until it gets dark, then he can't change the channel, the volume works, so it seems to be a problem with the DVR. Then he says that if he turns on the light, it works again. I can't think of a single explanation for this, but he says it happens every day.