If you have already tried to hold both the power and the nook button and it hasn't turned on you should seek out a replacement.
1. Hold the Power and the Home button for several seconds.
2. The nook will go into a Factory Reset screen with instructions.
3. I backed out of the Factory reset screen by pressing teh power button and my Nook HD came up running.
4. You can reset the nook to factory defaults if you the previous step did not work.