Sync Problems

Hi There!

I have an IPhone 5s running version 7.1.2, a laptop running windows 8.1 and the latest version of iTunes ver 11.2.2.3

I connect my phone via cable to the laptop and try to sync to update my music and although it goes through the motions, nothing actually changes on the phone! My phone shows 7,000+ music files, but I am only trying to sync around 2500? Any ideas what could be wrong?

Thanks

Phil