It might be worth posting at the iPod forum to ask what the problem might be. I've posted there myself (actually the iTunes forum.)
Be aware that iTunes does not recognise mp3 Pro format. But it's unlikely all your songs are in that format unless they originate from the same source.
Are you using windows or mac?

So you did try to manual add them to iPod? http://www.apple.com/support/ipod/tu...tarted_t3.html

You can go here & click on the forums link: http://www.ilounge.com/index.php/art...ned-and-rated/

By the way, mp3 is mpeg. It's a type of mpeg audio format.