Make sure the songs that you want synced are checked if you manually manage it, but i recommend auto, if you dont mind all your songs on your library being up there. You may have to restore you ipod which can be done easily by right clicking on the device and clicking on restore. My sister had a simmilar problem her songs refused to sync, and only a few of them would show up. If not try Ctrl+A in your iTunes library, and then right clicking, and clicking on "Create an AAC Version", and convert all your song to that format and try syncing again. Hope this helped.