While these are very good receivers, the software does lock up from time to time. Try leaving it unplugged for several hours, and it that does not work try overnight. Also disconnect the antenna cable, since I believe static electricity can sometimes accumulate in the antenna wire and cause problems if allowed to build up.
Also try other outputs (composite, S-video, etc) and see if you get a signal out of any of them.
If it still does not work, I would try to apply the firmware update, since you would really have nothing to lose at that point. I would recommend using the latest version you can find, since there were some audio problems that were fixed in the later versions.
I have not heard of very many of these units dying, but I guess it happens eventually.