itunes reinstalled - lost all content, want to get back?!

I recently re-installed I-tunes onto my pc. Once complete it had no content in it anymore, it had not retained all the music etc I had purchased and stored on iTunes. Is there a way of salvaging this? It has let me log in and has my details, but nothing else unfortunately.

My ipod nano still has music on it, which I would like to try and get onto my iTunes, without losing it if there was a way?

Appreciate if anyone can help 🙂

Thanks!

Nic