When connecting my iPhone 4S to my laptop via a cable, my phone is charging but my itunes is saying nothing has been connected and therefore i cannot sync anything onto my phone

I have an iPhone 4S and recently when i have been trying to sync my phone and laptop it is not working. I connect my phone and laptop via USB cable and then my phone begins to charge. It asks is i trust this laptop and i agree to trust it. Then i go on to my itunes hopeing to sync my music to my phone, but it says there is nothing connected. Usually a tab would come up saying 'Hayleys's iPhone' but now there is nothing there and i am not sure why. Please help!