Why my yahoo email address worked but my husbands did not with our new home computer windows vista/window mail?

Its a new HP home computer package that came installed with Windows Vista and has Window mail. We both have had our yahoo email addresses for years. Mine works with the windows mail and his does not. We have followed the pop and smtp server info but his still does not work and we keep getting error messages.|||maybe he changed his password and didn't tell you or he doesn't remember changing it