Outlook Problems!! HEEELLLLP!!

I have an NT 4.0 network, and am running Exchange 5.5…we have no internet access, so it’s only interoffice email that we deal with…today, a lot of our users cannot access Outlook…it just freezes at the hour glass when the program first begins to start…I can’t find anything wrong, and I’ve an angry horde here!! Help me please!!