Try doing a search for 'scanpst.exe'. Run this file and it will try to
repair the pst. You can also go into Tools>Services, then into the Delivery
Tab and remove the Personal Folders. Then from the File menu choose to
import>data from file (something close), and choose pst. It will then open a
window so you can browse to your pst file (make sure you do a search for your
pst beforehand so you know where it is). This basically removes the personal
folder file from Outlook and then imports the information in again. Pst's
are generally very touchy once they go bad, but try the repair tool and see
if it works. If not, remove and import it and check it again....if it still
doesn't work you may just need to remove it and make a new one. Cheers.