Outlook 2003 address book missing

I've started having a number of problems with Outlook 2003. The latest is that when I want to create message and click on the To or Cc boxes, the Select Names box opens but there is nothing in the Shows Names from the: box, and the To, Cc and Bcc at the bottom are all greyed out. I've tried all kinds of things but nothing works. However, Contacts still has all the info in it so if I type a name in the To or Cc box, the email address appears.

Outlook 2003 address book missing