Hello, I’m Nathan, and I’ll be assisting you today. My livelihood depends on your positive feedback, so your satisfaction is my highest priority.
Sorry to hear you’re having trouble.
If it reset itself, it was due to a hardware problem or software glitch.
Your items are not lost though.
Just follow through the initial setup prompts (connect to wifi, sign in to your b/n account) and your nook should automatically SYNC your prior purchases and download your books automatically.
This symptom can indicate several possible issues: an internal hardware failure, a low/faulty battery, or just a simple memory/firmware glitch.
The first step here will be to attempt to reboot the nook. This is done by pressing/sliding and holding the power button for 30+ seconds, then release. Give the nook about a minute to start back up, then run through the wifi and registration setup again.
If you can tell me specifically where you're getting stuck, I can help you through.
Try rebooting your router as well (unplug power 60+ seconds),
if still no change, then yes the nook would ultimately require service, which really means replacement (they generally can't be repaired).
You'll want to talk to b/n about warranty options at that point.