iPod nano 4th gen - itunes won't recognize music on ipod

So, I have an iPod nano 4th gen which I've had for a lot of years. Still works fine. I had forgotten my iTunes account info. Used the nano to get me back in to the system and can buy new music. However, the music on the nano won't sync to my iTunes account and the music in my iTunes account (new purchased music) won't sync to my nano. Thoughts?

ITunes software is current.