Try the following.
First: Leave the Nook plugged in over night.
It doesn't matter whether it's off or on. Just leave it plugged in.
Second: Press and hold 'power button' for 30 seconds. Then press and hold power button for 4 seconds.
Third: Press and hold power button and physical 'n' button for 30 seconds.
It seems that your Nook was in the process of updating and got stuck. Biggest thing is to leave it be when it restarts and when its charging. Just let it be for a bit.
this solution doesn't work!