Windows Live Mail not working

Having accomplished the change from Dual Boot W7 and XP to Single boot W7 (see my thread Problem reverting from Dual Boot to Single Boot) I am at a loss to understand why WLM is no longer functioning. It is almost as though WLM has been re-installed, but I certainly have not done that.

When I launch WLM I get an error message "Unable to send or receive messages for the Chaldon.plus (my.name) account. The host 'mal.plus.net' could not be found. Please verify that you have entered the server name correctly.

Server: 'mal.plus.net'
Windows Live Mail Error ID: 0x800CCC0D
Protocol: POP3
Port: 110
Secure(SSL): No
Socket Error: 11004"

The server name is wrong, and having corrected it to 'mail.plus.net' (my ISP is Plusnet) and clicked on 'Send/Receive All email accounts' I then get a window: -
"Logon - Chaldon.plus (my.name). Please enter your user name and password for the following server". This is already filled in with server name 'mail.plus.net' and dots for the password. I retyped the password in case the one pre-entered was wromg but after clicking OK the same Logon window keeps re-appearing.

When I set up WLM I did alter the location of the Store but at the moment cannot remember exactly where, but almost sure it was a sub-folder of Data Files folder on M: drive. When WLM opens the left-hand pane shows only one account (Chaldon.plus (my.name) together with Quick Views, Outbox and Storage folders, but there is no sign at all of the accounts I set up for myself and my wife and the very many sub-folders on both accounts.

Any thoughts on what has happened here and a solution to the problem would be welcome.