i know you said itunes isn't showing it but just try plugging it in and as the guy above said put it in DFU mode.
just incase you dont know how to do this , hold the top button and the home button for 10 second , then let go of the top button but keep holding the home button for about another 8 seconds , this SHOULD cause the computer to detect it then simply restore it , although restoring it takes such a long time

good luck with it , hope you can get it working again