I had the same problem with my HR20-700 this morning. Hit the reset button...booted up fine.
Had the problem this morning on my 20-700...power cycled it and it started working again. I then left the house for work and came back and it wouldn't turn on. I power cycled it again except before I plugged power back I pulled the access card and re-installed it. So far so good except now I have a message on the info screen that says to replace the access card when I receive a new one.