iTunes not recognizing iPhone 4s.

Hello, So I plug my iPhone 4s into my computer, and I have tried multiple USB ports on this computer, and my computer will recognize it right away and start charging it, but iTunes will not recognize the device, therefore I cannot sync. Although I can plug in my iPod Nano 2nd Gen (yes I know it is old but it works fine for me) and it will be recognized by iTunes just fine and I can sync. I am wandering if there is a plugin for iTunes that I need just for the iPhone 4s or.? It gets recognized and I can sync it just fine on my laptop, but on my desktop iTunes just will not recognize.

PS. My desktop is PC not mac.

Any help is greatly appreciated! Please!

Thanks,

Eric