Sounds like it is not charged. Plugged into the USB of your computer it will actually dis-charge unless the computer is actively on (in other words not "sleeping" or in "hibernation". Ether use a barrel connection AC charger (PSP or one made for the reader) or keep your computer active for a few hours to charge it back up.
No point in just letting it sit there, the battery is already dead.... you need to charge it...
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