It could be the battery but try resetting the Nook by pressing and holding the power button for 20 seconds. Let me know if it still fails to react.
Now try this. Try a deeper reset. Plug the Nook into the charger for 30 minutes. After that AND WHILE STILL PLUGGED IN, press and hold the power button for 30 seconds. Do not disconnect the charger throughout the process. After that, try using it.
I will be here.
Can you provide the model number off of the back of the unit? The batteries last 2-3 years and you're beyond that...so I'm assuming that's the problem because you don't have any display issues.
This is the battery with instructions that you need. https://www.amazon.com/Replacement-NOOK-HD-BNTV400-Installation/dp/B00QO6AW16/ref=as_sl_pc_ss_til?tag=thcosezo-20&linkCode=w01&linkId=NMAWNYZ4F2F47NY7&creativeASIN=B00QO6AW16
Have a great week.