iTunes not uploading new songs to iPod Nano 6th gen.

My iTunes is updated with the latest version but when synching with my iPod Nano 6th gen. it doesn't upload any new songs. The iPod's on/off button has broken a second time and maybe it's reached the end of it's days. But any ideas on why the synching doesn't upload? If I were to buy a second-hand 6th Gen iPod would it still work with iTunes?