ACK! First, never call the 1-800 number. I don't know what kind of training they're getting (about as bad as some stores, but that's a long story),. If you're in the store, find someone who knows stuff and have THEM call the in-store support people. They're not much better, but we get paid to put up with their lameness and can filter out bad advice.
Second, I have some bad news. By deregistering, you've wiped the nook clean. It saved your notes and highlights from your BN library, which is synced and remembered. I popped up the default wallpaper, and your BN books will show up. Everything that is not from B&N is gone. I so so hope you have it saved somewhere. Library books will still be under Adobe Digital Editions. Everything else will have to be loaded again through your computer.