Windows mail set up probs

[#1]

Just got a new laptop and cant seem to setup my windows mail.  Have set up the email account as instructed on the plusnet website and seem to have received emails into my inbox but whenever I try to send email I get the following error message:
An unknown error has occurred. Subject 'TEST EMAIL', Account: 'mail.plus.net', Server: 'relay.plus.net', Protocol: SMTP, Port: 25, Secure(SSL): No, Error Number: 0x800CCC0B
I havent accessed my plusnet email for some time if this may be the cause?
Thx

[#2]

In the User Name box, are you sure that you have have just put in your uername and NOT the entire e-mail address?

[#3]

OK a couple of things:
1) You are definitely on a PlusNet IP when you were trying to send?
2) Make sure you have not enabled SMTP authentication. This is not needed for PlusNet.
3) Make sure you have not set SPA (Secure Password authentication).
4) Turn off any anti-virus software temporarily in case that is blocking SMTP.
5) Turn off any firewall temporarily in case that is blocking SMTP.
6) Try using telnet in a DOS box
telnet relay.plus.net 25
You should then see something like the following:
220 relay.plus.net ESMTP Exim Sun, 19 Aug 2007 09:32:35 +0100
If not something is blocking port 25