Prodigy (and some other) ISPs: Some ISPs require Client for Microsoft Networks installed and selected as your primary network logon. (Windows: Control Panel->Networking)
AOL on your system? If you have AOL installed on your system, but are not using AOL, the AOL software may interfere with access to any other ISP. Uninstall AOL. (Windows: Control Panel-> Add/Remove Programs)
Delete the connection and make a new one.