I've had this box for about 3.5 years and a few days ago it started exhibiting this issue. We will find that the box is unresponsive (no lights on the panel and nothing but a black screen on the TV). There is, however, a red light in the back and sometimes even the record light still shows but the fan isn't running. If I unplug the box and plug it back in, the fan will start-stop-start-stop... forever. I typically have to try this several times with a wait in between before the box will again start normally and everything is fine for some hours before this happens again. We haven't actually been watching it when it goes down so I don't know if an error message is displayed, etc.
My first thought was that the box might be overheating although there was no real reason it should have. As a test I pointed a large fan at it and kept it running. The temp, when I checked it, was in the very low 100's (F). However, when I came back about 6-hours later it was shutdown again and the box was very cool. I have never seen an overheat message either when on for a while or when restarting from this issue. Interestingly though it was much easier to restart after the fan test as I only had to unplug it once. Could have been a coincidence. My only other thought is a potential power problem but of course that is a guess.
Certainly I can call DTV which I am sure will result in them sending me a new box for money. I have recorded programs on this box and hate to do that so first I wanted to see if anyone else has run into this.