You will have to go through your email provider to have your password
reset - some have a "Forgot Password" link if you go directly to their site
to login. I suspect you had previously used the "Remember Me" features in
your account setup so you didn't have to enter your credentials. Now that
you've switched services, all that got reset to the default values and
that's why you are now being prompted to enter it. Check your account setup
in WM (Tools - Accounts) to see what other info you may be missing (servers,
ports, etc.). Yahoo has some "special" issues (i.e. need paid-for version .
.. . . ). Also, if you cancel out of that login and get any error messages,
you should cut-n-paste them into this for more precise assistance.