When i go to yahoo email i get told the security certificate has expired or i dont have one also my date and time is at january 2002 can you help thanks

Most security certificate are valid for a year or two. If you computer's data is out of that range it will assume the certificate has expired or hasn't yet become valid.
The first thing to do whenever you have certificate errors especially on secure websites is to check the clock.

Right click the clock and click adjust time/date and make sure the Time.....the Day....the Month and the Year are all correct....and finally check you are in the right time Zone.

While in Internet Explorer, click "Tools" > Internet Options > Advanced. Scroll down to the "Security" section and uncheck the "Check for publisher's certificate revocation" box.