If you log into your Yahoo mail account at the website, they should provide instructions on how to set up access to the account through various email clients. Windows Live Mail should be one of them.
As for the attachment issue, is the server bouncing back the message at all? Is there a description of the problem in said email?
I used Windows Live email prior to the upgrade so my servings are correct. Re. the attchments, nothing happens when I try to email a scanned document or picture. I CAN insert what I want but the scanned items will not go from the scanning program. I would think it's my scanner program but that wouldn't explain the problem with yahoo mail. When I access my account I cannot open the inbox or spam unless I right click and even then I cannot delete any of the messages. I am so frustrated. Thanks for your help.