Solution #1
Completely power off the NOOK then press the "n" (home button) during power on. This should get it unstuck. If it doesn't work, drain the battery and once completely drained, charge your device and power on. The battery should drain quicker than usual due to the 99% screen being active.
Solution #2
Hard Reset. The following procedure details how to perform a NOOK HD/NOOK HD+ factory reset. A factory reset will de-register your device, removing all digital books and files, including side-loaded content. The titles you have purchased will remain in your account.
NOTE: It is recommended that all side-loaded content you wish to save is backed up to an SD card or computer before proceeding.
To Hard Reset NOOK HD:
1. Confirm the device is powered off.
2. Hold the Power and Home key simultaneously.
3. Release the Power and Home key once the NOOK logo appears.
A Factory Reset prompt will appear.
4. To continue, press the Home key.
5. To exit, press the Power key.