Gary,
This is what I found regarding Yahoo using POP3 settings..
Yahoo! Mail Settings
Unlike Hotmail, Yahoo! Mail offers standard POP3 access for receiving emails
incoming through your Yahoo mailbox, by using your favorite email client
software. To setup your email client for working with your Yahoo account,
you need to select the POP3 protocol and use the following mail server
settings:
Yahoo Incoming Mail Server (POP3) - pop.mail.yahoo.com (port 110)
Yahoo Outgoing Mail Server (SMTP) - smtp.mail.yahoo.com (port 25)
In that case, you probably have a free Yahoo account.
US-based free Yahoo accounts have webmail access only, no POP
access. Windows Mail does not handle Yahoo webmail.
There are two possible solutions:
1. How did you access Yahoo mail before? If you are happy with
webmail via your browser, you can continue to use that.
2. Pay Yahoo to get their premium "Mail Plus" service:
http://help.yahoo.com/l/us/yahoo/mail/original/mailplus/overview/index.html
and use the special settings for that service:
http://help.yahoo.com/l/us/yahoo/mail/original/mailplus/pop/pop-14.html
There is a third option called YPOPs, but I don't recommend it any more
because it is not reliable.