I was using my kobo when all of a sudden it turned off. I tried turning it on, but it seemed to be out of battery. When it turned off it still had about 30-40% battery left. Anyways, I plugged it in an it still won't turn on. :/ I haven't damaged it in any way other than a little scratch, and it hasn't been acting up or showing any signs of misbehavior. What should I do?