Have you tried doing a factory reset using this method:
- hold the power button slider in the "on" position for 20-30 seconds,
- release it,
- hold the light button down and use the power button slider to turn it on while continuing to press the light buttom.
All of your settings and the sideloaded epubs added into main memory will be gone after this. You will have a new and empty database. You will be starting over like with a new device.