I don't know how far we can go with this. If you've talked for months with the manufacturer, and they even went through the trouble of sending you a new one, it should have worked if it's going to work at all. The best I can tell you is to fix disk permissions and/or create a new user account to see if that does anything; make sure you have all the latest updates from Apple, make sure that your Finder is set to show USB drives (Finder:Preferences:Sidebar), and make sure that your MP3 player has all it's newest firmware and is not set in a mode where hard disk recognition would fail.