I can't sync my 160gb iPod Classic to my iTunes library

I have a 160gb Classic iPod. My iTunes library has about 100gb of music. My iPod is set to sync my entire music library. When I connect my iPod and press 'Sync' I get the message 'Syncing - step 1 of 1' and then 'iPod sync is complete' - but there is no music on my iPod. I am running Windows 8.1

Help, please!