First of all, yes, you can take the Nook to a B&N store. The employees will be happy to assist you.
When you have the Nook charging, is the charging light next to the plug on the bottom orange or green?
When you attempt to turn it on, is there any activity on the screen, or does it remain completely black?
Try this: Press and hold the power button and n button simultaneously for 20 seconds. Wait for 15 seconds for it to start automatically. If it doesn't restart by itself, then press and hold the power button for 4 seconds.
Hope you get this fixed. Don't hesitate to take it to your B&N store.