Well, you could try reinstalling IE, which contains Outlook Express, or you could try downloading a different mail client, such as
Thunderbird, to see if that will work, but unless anyone else has any brilliant ideas, it sounds to me like you may be fighting a losing battle, and the only way might be to back up everything you need, format and re-install Windows. It might sounds like a drama, but it will take a few hours, whereas you've already spent at least two days on this, and how much longer are you likely to spend trying this, that and everything else?
