Kindle 3 Problems: Frozen on Critical Battery Screen?

Last Christmas I was given a Kindle 3. I use it very often, but lately noticed that the battery is going dead quite quickly- within less than 12 hours between charging and it being completely dead, regardless of whether I read or not. I figured the battery needs replacing and I have been procrastinating. Tonight, the Kindle was displaying the Critical Battery screen, as per usual. I let it charge for a few hours, the light was green, but... it's still stuck on that page, except for a corner at the bottom of the screen that just looks like lines. I tried to do a hard reset, nothing. The light is green, so it's fully charged. Anyone know what I need to do?