There are a few tweaks you can try --short of a reinstall of OE
see here:
An Outlook Express basic repair kit
I would try the reregister OE & Reregister Libraries commands about half way down
If they don't work I would try creating a new identity in OE.
Without that disc-- a reinstall is not possible.
You might be able to borrow a friend's copy-- use his setup & YOUR registration key.
If not there are a few good free email clients...Thunderbird or Eudora
Comparison of e-mail clients - Wikipedia, the free encyclopedia