that happened to me!!
i hated that
i have verizon, [actually my dad had a problem with his ipod where the songs wouldnt go into his ipod]
but what we did for his problem [mine got solved with a new router...], was we saved his itunes libary in a totally diferent file, then we did what jaz said, and uninstalled itunes, then reinstalled it. then dragged the files back in. nothing was deleted. and then his ipod worked fine, what you might have to do though, is just email apple, they would probably be more helpful than circuit city or best buy [see above post
]