I recently turned on file sharing so I could use my newer computer instead of my old desktop for itunes/ipod. Now my ipod won't automatically sync on the new computer. The option to sync is not even highlighted under the file menu, so I can't choose it. Do I have to de-authorize my old computer? I haven't been able to find how to do that if that's the case. I'm running Windows Vista on the laptop and Windows XP on the old desktop.