First try to reset the Nook by pressing and holding the power button for 20-25 seconds. Once it's turned off, let it sit idle for 5-10minutes. Then press the power button for 3-5 seconds. Wait for the Nook to turn on.
Also, try the reset procedure while it is connected to the charger.
If that doesn't solve anything, you may want to try Factory Reset but that will make your Nook lose all downloaded books(although you can get them back again).
1. Tap on the Settings
2. Choose Device
3. Choose to Unregister your Nook
4. After you unregister, choose to Reset to Factory Settings(Under the Unregister option)
Another option is replacing the battery. But that doesn't guarantee it's longitivity.
You can get the replacement battery from the link below.
If all fails, I'm sorry, you will have to get another one, either a Nook or anyother e-reader. The reason is, a repair will cost you as much as a new one and since there is no warranty, ou will have to repair it by paying out of your pocket.
I have listed out all the possible options. If you have any queries, please do not hesitate to ask.
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