Fix UI stopped working on Nook

Try to reset your unit or update to the latest version.

if your have faced this issue while using your computer. Then you need to follow these steps to fix UI Failed to Load on windows

https://www.mygeekshelp.com/avast-ui-failed-to-load-after-windows-10-update

Barnes & Noble stopped doing APPS. they still do book.
Other books can also be put on you NOOK. Project Gutenberg now has over 30,000 free titles. You basically download onto your computer and read it using Calibre, a free e-reader. Or, then plug the Nook into your computer and transfer the e-book to your Nook. The non-B&N books can't be in the same place as B&N books, but you can make separate folders under My Files. For other books, if they are epub or PDF, you can read them on Nook. (Comic books are often in .cba, .cb7 which can also be read.) Some sites (Google Play and LULU for example) have multiple formats and it is not easy to learn which will work on your Nook.

There are two methods to reset your nook device:
Just follow the link and reset with these simple steps
Hard Reset Procedure For Nook Users

Have you checked the restriction settings on your Nook? Try checking to make sure the restriction settings have not been accidently turned on for the browser.

1. Press the ? button to display the quick nav.
2. Tap Settings.
3. Tap the Security option.
4. Tap Restrictions.
5. Tap the Restrictions check box.
6. Enter your four-digit code for Restrictions.
7. Tap the Browser check box so that it's not checked.

Hope that helps!

Go to settings, then device information. While pressing the volume up button, tap above the volume bar and a popup menu will appear. Uncheck "Enable demo mode", then power down your Nook. When you restart it, the Nook should be in regular mode.

Try going to your Apps settings and uninstall Google's updates. If that doesn't work, try uninstalling Google completely and then reinstalling.

try to hold your power button and home buttom at same time or 1 min it will rebooth it

TRY a hard reset on the Nook if that doesn't work i know of this fantastic site BNTPrice.com that sells them for cheap. i hope this works for you

1. Press the "n" button to display the quick nav bar.
   

2. In the quick nav bar, tap the Settings icon.
   

3. In the Device Settings section, tap Device Info.
   

4. Tap Erase & Deregister Device.
   

5. Stop. Think. Think again.
   

6. If you really, really want to do this, go to Step 7. If not, tap the Back button.
   

7. Tap the Erase & Deregister Device button.
   

I think you need a new battery.