Without further explanation, pictures or details of what you tried, it's hard to tell what exactly is wrong with your Nook. However, assuming that the battery is still good you will need to "reboot" your Nook.
Unlike other tablets, there is no reset button, but you can try this.
While pressing the Nook button (upside down u on the front of the tablet), press the power button on the side. You will need to hold it for couple of seconds.
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