I Can't add music from iTunes on laptop to IPhone 4s?

I have tried adding music to iPhone 4S but it doesn't seem to transfer to my iphone I have switched it on and off and disconnected and connect it and syncing it but none of it has work anymore ideas anyone?

What operating system you running?

One reason could be the version of itunes your running from. You should check to see what kind of version your iphone is running on, and then update to be that or higher.