BST,
have you tried to update manually and was it successful?
Have you checked that your year is already set to 2004?
Have you checked in control panel that your date/time format is "ok"?
Have you checked in control panel that your international settings are correct?
Are you, or have you ever, run any dodgy software for calendars other than the Julian one (Moslem, Jewish, Chinese etc.)?
These are just off the top of the head, and if I get a chance to dig deeper, I'll ask some more inane questions later
ST