i had the EXACT same problem yesterday! turns out my chord was broke. it had gotten stuck under a heavy object and that apparantly ruined the insides of the chord cus the outside looks fine
but anyway i got out an old and still-in-good-shape ipod usb chord and it worked fine and my itunes was able to recognize that i had my ipod plugged in
do u think anything might have happened recently to mess up your chord? you might need a new one
i ordered one with free shipping for $2 off of ebay
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insanity is what keeps me sane