There's a known bug in the reader, where it won't shutdown properly and so keeps draining down the battery (without the user being aware) until there's almost zero charge left. I've had this happen about 4 times in one year.
But this draining should take some time, I'd estimate at a minimum 2 to 3 hours (if it runs at maximum cpu load), but probably more like 8 hours. How much time was there between when you shut it down and then tried to start it again?
And have you used the reset button before and did it work then?