Does your PC see it, but just not iTunes? (Right click on "My Computer", select "Properties", find the tab with the button to get the Device Manager, and look for it there.)
Are you connecting it with a cable, or directly to your computer? Try it with a different cable, or in a different port.
Take a look inside the USB connector – does it look OK?
Do other things work OK with that cable/USB port?
Do you have the latest version of iTunes? Have you tried reinstalling it?
If none of this helps, can I suggest
this link?
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