It's that old so I won't bore you with the backup of the PST. But you can remove OL2003, reinstall it then that very much needed SP3 for Office 2003 and it should work again. If not, look up the old /A and other commands. I'll keep this compact since it's a very old item so most folk just need the reminders.
I have Windows Vista, Outlook 2003, and Microsoft Office 2007 home and Student. Yesterday Windows updated with about 10 updates and now my Outlook messaging doesn't work. When I click on New Message, the message window comes up without formatting buttons or Send or Forward, etc. I can create messages but not send them.