When I plug my iphone 4s into my Windows based computer, itunes does not recognize it. I've rebooted both, and still nothing.
I've updated itunes also.
Please refer to this Apple support document:
The same thing happened to me. If you click support on the apple website and then click iTunes you can click devices and then it will show you a link to what you can do to help.
Hope it helps!!:)
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