To repair your PST file, you’ll have to open the Scanpst.exe utility that’s included by default with Outlook. The only problem is that there’s no shortcut to it, so you’ll have to find it in the Outlook folder.

Open up explorer and then browse down to the following folder for Outlook 2007:

C:\Program Files\Microsoft Office\Office12

Or one of these folders for Outlook 2003 and earlier:

C:\Program Files\Common Files\System\Mapi\1033
C:\Program Files\Common Files\System\MSMAPI\1033

Once you open up the utility, you’ll have to find the location of your PST file by clicking the Browse button.
It will take a while to scan the file, and you’ll get a report at the end telling you whether you have errors in the file.

Click on the Repair button, and after a while you’ll finally get the “Repair complete” message.
If you are curious what was actually repaired during the process, you’ll find a text file in the same directory as your PST file with the same name as the PST file.