My iPhone 5s is not syncing with itunes library.

Everything is up to date. Everything has been rebooted. I've tried by wifi and cable. But my iphone 5s will not sync with itunes. It keeps running through the process of syncing until it gets to step 4 of 4 "Waiting for changes to be applied" then it just stops... I am trying to add some audio books and music. When it starts the sync it gets to step 3 and indicates that I only have 39.18 GB Free on my iphone but after it stops at step 4 it reverts back to 49.73 GB Free. I've ready several of the discussions but haven't been able to get it to work. I have a PC running Windows 7 with iTunes.