iTunes library not updating.

I recently upgraded my version of windows, but before I did this I made a backup of my library. unfortunately something got messed up with the backup im not sure what, but anyways when I sync my ipod to iTunes none of the content on my ipod gets erased. New stuff comes over but nothing goes to my I tunes library. my question is how can I update my library to have the same music as my ipod? any help would be great thanks.