Why does my replacement iPod nano 7th gen not sync?

I've just got a replacement iPod nano 7th gen after my last one was faulty (suddenly having white screens etc) - exact same model type. I've charged it, and when I put the new replacement iPod in the computer it makes the regular sound to let me know its recognised the iPod. The iPod shows the 'connected - eject before disconnecting' sign so that part of it seems to be working.

I then go to devices looking to sync the music into my new iPod and then when I do that the 'Sync' button is grey and will not let me progress to sync. This is the problem I am having and I need help.

Let me know if you need any more information, thank you.