You need to replace the files from the itunes library folder called itunes library, the xml file and the extras file and the genius files( basically all the files not folders) on the computer that isn't already synced. It will populate itunes with everything(even files that aren"t there. Just delete(from itunes) but don't trash the files. Then drag your itunes music back in and you're good to go.
holy cow...that sounds so confusing im lost
i dont have the itunes library file tho..
where is it?
i had to format my computer