Ok, is this a workstation on a network or a stand alone on a dial up? What OS is it running and what version of Outlook? If networked, perhaps all you need to do is delete the mail profile and re-create it. Check the mail profile in the Control Panel, Mail applet, and show all profiles.
If it's Outlook that's not running (I mean the program won't run, not that it cannot find the mail account or wants to set up a mail account) then simply try to re-install or repair Outlook using the software originally used to install. Any patches, critical updates, etc. will need to be re-installed also. Post more comments if necessary!