ON OUT LOOK EXPRESS A DIALOG B APPEARS SAYING THAT I HAVE TWO UNSENT
MESSAGES. DO I WANT TO SEND THEM NOW? I RESPOND TO EITHER "YES" OR "NO"
IT STILL POPS UP AGAIN AND AGAIN. WHEN I CHECK THE OUT BOX FOR
MESSAGES ,THERE ARE NONE?

if you are using internet explorer 5.5 or 6.0 you can go to add/remove
programs in the control panel and click to remove internet explorer.
A dialog box will open asking if you want to remove it or repair it.
Select the repair option.
You will need to reboot your computer. (outlook express is a part of
IE and will also be repaired)
You might also try a virus scan.

You also asked this question in the computer section (ID 9477)..
here's my comment again:

You likely have some kind of problem with your outbox that causes
messages to get stuck there. So even you answer 'yes' and Outlook
tries to send it again it'll fail and the messages are still there
causing the same popup to alert you again and again.
 
There's a Microsoft knowledgebase article, Q262052, for Outlook
Express that explains some likely problems and solutions for your
Outbox problem. The URL is:
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q262052
 
You might also want to browse through the Outlook Express support
pages at Microsoft: http://support.microsoft.com/default.aspx?scid=fh;en-us;oex