Outlook files are PST files By default, Microsoft Outlook stored these PST files at the following location:
"C:\Documents and Settings\USER_NAME\Local Settings\Application Data\Microsoft\Outlook\", where USER_NAME is your Windows logon name. The default PST filename for your active mailbox is Outlook.pst, while the archive file is stored as archive.pst.

Navigate to the above directory and copy the files and save them to a safe place on your computer such as "my documents" folder. Do not just move the files...make a copy and move the copy For back-up purposes.

Go here and follow the directions closely. It maynot work in your situation but worth a try.
How to find and run the Inbox Repair tool in Outlook

If it doesn't work then you need to do a system repair using the Microsoft Office installation disc... This will reinstall the program and save the files but sometimes the files are unsaveable...thus the back-up!