You cannot transfer song files from iPod to computer using iTunes (except for songs purchased from the iTunes Store). However, there are third-party methods and utilities that can transfer song files from iPod to computer. If you do a Google search on something like "ipod transfer," you should get some links.
NOTE: Songs previously purchased from the iTunes Store can also be re-downloaded at no cost, from the iTunes Store Purchased screen.
This site contains user submitted content, comments and opinions and is for informational purposes only.
Apple disclaims any and all liability for the acts, omissions and conduct of any third parties in connection with or related to your use of the site.