I want to restore it, but cannot since it does not appear in iTunes
Try these steps in the first article below. If the issues still persists you might have to reinstall the Apple Mobile Device Service. The second article I have included, goes through the process of the reinstall.
iPod not recognized in iTunes and Mac desktop
iTunes: How to remove and reinstall the Apple Mobile Device Service on Mac OS X 10.6.8 or Earlier
Retrieving data ...