For starters I would try uninstalling Nook and see what happens. Fortunately it doesn't sound like a hardware issue so you may to do a fresh load of Dingo or Ermine (whichever OS you are using). Of course if you can move forward you will want to do a Local Backup of your Library to a USB drive. Also, if you have ES File Explorer you may want to copy and personal folders to a USB drive. Here are the links in case you can't get this resolved. Remember, this should be your last resort.
Ermine:
https://www.entourageedge.com/suppor...barticleid=265
Dingo:
https://www.entourageedge.com/suppor...barticleid=263