Thanks for the update.

My mother has a Sony 505 and this happened once to her. I think she let the battery drop too low, and when she tried to turn a page it stayed on "loading". She said it was still on half charged before it happened.
I still have no idea why it was stuck on "loading", but I tried to charge it with her computer, but it still said "loading". I do know that when our computer went into sleep mode that the battery would drain and not charge.
I just took her Reader home with me and used a wall charger to charge it over night. The next morning, when I unplugged it, it still said "loading", so I just left it on the table to see what would happen. Two hours later, it was up and running. I still have no idea what happened.
I hope you get yours up and running again. Keep us updated.