As in the cases people already described, and some others I won't go into, it is NOT as simple as unchecking a preference. Also, try plugging your USB hard dis

As in the cases people already described, and some others I won't go into, it is NOT as simple as unchecking a preference. Also, try plugging your USB hard disk into a different USB port in a different order from your iPod. Now it comes up with a different drive letter and iTunes can't find any of your music.