I am receiving but can’t send emails

I followed the recent similar thread to see if that would help, but unfortunately not.

I have been using live mail for as long as I can remember mostly without issues but today I'm not able to send emails from my main account. I am receiving emails ok.

If i try to send an email to anyone and/or myself, i get a window asking me for my account name and password. Both fields are already completed with the correct info (I can't actually see the password but I'm able to enter it again to make sure it's the right one).  The window disappears for a few seconds, then comes back. This repeats ad infinitum.

I'm sure the password is correct (it's the same for all my other device email applications (phone, tablet) and those are all working), and I'm receiving emails ok.

There is no error message, just the continuously appearing window asking for user name and password.

Please advise.

Here is a screenshot of my advanced settings

And this is the info from the Live Mail about -

Version 2012 (Build 16.4.3528.0331)

Copyright © 2012 Microsoft Corporation. All rights reserved.

Microsoft® Office 2010 Proofing Tools

© 2010 Microsoft Corporation.  All rights reserved. 

Any help would be appreciated