My iphone is not being recognised by itunes

I bought a new Toshiba wih Windows 7 and my iphone 4 is not being recognised by itunes but my ipad 3 is. How do I fix this?

I have uninstalled and reinstalled itunes 3 times but it hasnt fixed it. Its not my cable as my ipad works and I can charge my iphone from a power point with the same cable. My computer is recognising the phone as it beeps when the cable is connected. I havent been able to sync my phone for ages.