Outlook 2000 shuts down several times each day without notice.

Outlook 2000 has begun shutting down several times a day with no error
messages or notices.

Check your application event viewer.

Check your application event viewer. Try running Detect and Repair from the
Help menu (you may need your installation disk for that), try checking the
size of your PST (Outlook 2002 and older have a size limit of 2 GB), try
repairing your PST.

http://www.howto-outlook.com/faq/aboutpst.htm