Connection trouble with mail

I have an iMac aluminum 20" 2.0ghz, all normal specs, that I purchased before the release of Leopard. When I installed Leopard the installer crashed and ruined the operating system, and continued to do so every time I tried to run the installer. I was able to recover the files via firewire, reformat, and it installed like charm, however Mail and iChat will not connect since the install. I can connect to the internet via Firefox or Safari, and have tried both the official apps, Mail and iChat, as well as third party versions, ie Thunderbird and Adium, and nothing will connect. I have tried connecting via Airport and wired, and on different networks, with no change. The firewall is completely off, and there is no other internet security installed. Anyone have any ideas as to what may be causing this?