The gentle options are to clear the caches of your browser and apps, and power the device down completely and power it up again.
If this doesn't help, the 'nuclear' option is to erase and re-register the device, which returns it to factory settings. Your B&N purchased content will download itself automatically when you put in the B&N account details used to purchase it. Likewise the Google Play store apps can be re-downloaded from there when you sign in, but you will lose Game progress unless you back it up- either via the developer offering the option or an app designed for it. Everything else you have loaded you would need to have backed up to a pc so you can reload it all again.
That's the bad news - the good news is that it really speeds the Nook up.
Hope you manage to resolve this....