When I click on Windows Mail to check for mail, I get this message:

The host 'mail.btinternet.com' could not be found. Please verify that you have entered the server name correctly.
Account: 'Windows Mail', Server: 'mail.btinternet.com', Protocol: POP3, Port: 110, Secure(SSL): No, Socket Error: 11001, Error Number: 0x800CCC0D

I checked the email settings and they appear unchanged. I am able to access my mail using BTYahoo mail. Can anyone help please as Windows Mail is my preferred client.

Have you ever been able to get windows mail to check that account? Are you sure that you have the settings correct? I haven't heard of BTYahoo but I believe that for you to be able to have a mail client connect to a yahoo account you have to pay for their premium account (see here).

It may not be much help, but I’ve had exactly the same problem since about November 10th 2009. It was working fine before then (i.e. downloading e-mails from my BT Yahoo Mail to Windows Mail), but suddenly stopped. I’ve tried everything to fix it, e.g. deleting my accounts and setting them up again, double-checking all the settings etc., to no avail. I had the problem once before – it just stopped working for about 2 months, then suddenly started working again. On that occasion it coincided with when BT Yahoo upgraded its webmail and introduced a new version. BT denied all knowledge of any problem at the time. I have had a similar problem recently with Barclaycard’s website, which didn’t work for several months when they upgraded their website, then suddenly started working again. They denied all knowledge too. I have contacted BT re the current problem, but they have not responded. It’ll probably start working again as suddenly as it stopped. They’re all a bunch of cowboys and I’m cancelling my account very soon.