Search your hard drive for a file whose extension is ".wab".  When you find
it, doulb;e click it.  The Windows Address Book should open.  Does it
contain your contacts?

Most likely you aren't actually using a full version of Outlook. You're
using IMO mode which actually uses Outlook Express for some of its functions
such as the address book. So your problem is actually within Outlook
Express, not Outlook.
You have two options to try to fix this:
1. Close Outlook. Open Outlook Express, then open its address book. Go to
Tools > Options. Disable sharing. Restart OE and then re-enable sharing.
Close OE. Open Outlook. See if your address book now works.
2. If not, you'll need to repair your Windows Address Book: close both
Outlook and OE. Rename any WAB32.DLL files you find. Then run a repair
operation on Outlook Express.