It is not unusual for the Outlook Address Book to "lose track" of the
connection to its Contacts Folder when you move or import your PST or update
your Outlook version or OS. Use the following steps to reset the connection.
Note that in some instances you may actually have to remove the Outlook
Address Book completely from your Profile, close Outlook, and then re-add it
before you can get it to work.

Go to Tools > E-mail accounts > View or change existing directories or
address books > Outlook Address Book. If it is not listed, back up one step
and add it. If it is, then click on Change. to make sure the Contacts
folder(s) you want to display are listed. You may need to enable the
Contacts Folder as an e-mail address book by R clicking the Folder >
Properties and check the "Show this folder as an E-mail address book" box.
Make sure you restart Outlook after making these changes.