Outlook and Outlook Express are known to have various limitations and bugs, some have been listed below.
Outlook PST files can become corrupted if your PC is hit by a power surge, power failure, lockup and other unexplained reasons. If this occurs while Outlook is writing to the Outlook file, the outlook file can become corrupted.
Step 1: Microsoft provides the Inbox Repair Tool for correcting most problems with damaged Personal Folders .pst files. If you do not see the Inbox Repair Tool on the Start menu, under Programs | Accessories | System Tools, use Start | Find or Start | Search (depending on your operating system) to search your system for "Scanpst.exe". Run this file when you find it.
Step 2: Find your PST file that is damaged by searching again as above, but this time, search for "*.pst", find the location of the file and put this location and filename into the ScanPST program.
Step 3: Run the repair tool. This will attempt to repair your Outlook file to a usable state. Once this is completed, you can try opening Outlook again, it is suggested to restart your PC before opening Outlook.