Fifth Gen. (late 2006) iPod has song files in its folders but will not show them in the iPod playlists.

I am using Windows 7 and the latest version of iTunes (x86). I just manually put a few hundred songs on my late 2006 5th Gen. iPod. When I check the hidden folders where the music is stored I see the hundreds of files, but they don't appear on the iPod playlists (Songs, Artists, Playlists). It appears empty, even though all the songs are being stored there, but is otherwise totally functional.