When you plug it in, what color does the light next to the cable turn?
If it doesn't turn ANY color... you have a bad charger so it's still dead. The computer will throw a fit with a discharged Nook because it won't respond correctly. Get a new charger (the NST takes ANY micro-usb charger so you don't need a special one).
If it's yellow,.. it's still not fully-charged. You have to wait a while (gift it an hour) after it completely dies.
If it's green... you have a problem. It's fully-charged and should turn on.