Well, keep in mind that the Nook & iPad are also computers - when a computer starts acting up, my first choice is to reboot! A few days ago, my wife said her desktop computer (Dell w/ Windows XP) was slow and programs were opening slowly - please reboot - she did & back to normal!
My iPad 'frooze' after loading a new app - do a 'reset' or then a 'reboot' - which worked to get the app working as advertised! A couple a weeks ago, one of our xray machines stopped working (I'm a radiologist) - the computers in the equipment run off a Unix OS - had to reboot but then back in business.
So, one of the simplest actions to take initially that often solves the issue in question -