This is generally better than trying to repair it using Scanpst or a commercial tool.
If you use Outlook 2007 or older and the pst file is in the default folder location, you can find it in the following locations: Windows 7/8 or Vista: C:\Users\username\App Data\Local\Microsoft\Outlook Type or paste this shortcut in the scanpst dialog to jump to the location: %localappdata%\Microsoft\Outlook Windows XP or Windows 2000: C:\Documents and Settings\username\Local Settings\Application Data\Microsoft\Outlook Type or paste this shortcut in the scanpst dialog to jump to the location: %USERPROFILE%\Local Settings\Application Data\Microsoft\Outlook See Outlook Backup and Dual-Boot for additional information on file locations and ways to determine the location of a file that you can see in Outlook.
See You Receive an Error Message When You Use the Inbox Repair Tool to Scan a File For seriously corrupted PST files, try running (look under Programs | Accessories | System Tools) first, then Scanpst.exe, repeating 3-4 times until neither program returns an error.
If the file is on an NTFS volume, you can't use so easily.
If do use try to repair an OST file and it's corrupted beyond the ability of to repair it, delete the ost.
When you reopen Outlook it will make a new ost file.
If it finds errors, it asks whether you want to make a backup copy of the original file (always say Yes), then tries to correct the errors.
If you run against a file that Outlook 2003 created for a local copy of Windows Share Point Services events and contacts lists, you will get an error message that you can ignore.