Why won't my iphone sync with itunes on my new MacBook Pro?!

I plugged my iphone 4S into my new MacBook Pro (Mountain Lion) in order to download some music to my iphone. My iphone icon shows up in itunes, but when I press the SYNC button to download my selected playlists from itunes to my iphone, nothing happens! What is going on? 😕 (I am not a new Mac user and have performed this simple action many times before with my old Vintage MacBook.)

I have already:

1) updated all software (lastest updates)

2) rebooted both my computer and my iphone

Any help with this would be most appreciated. Otherwise, it's off to meet with a Genius at the Apple Store!

Thanks! 🙂