Hello! My name is Sandy.I'm reviewing your question now. Let's get started!
A. Please go to the website http://mail.yahoo.com/ and see if you are able to login to your Yahoo email account.
B.Is this mobile an android phone or iPhone?
C. Change your Yahoo account password ***** enter the new password ***** the mobile:
Please go to https://edit.yahoo.com/forgotroot, and try to reset your Yahoo email account password.
Keep me posted and remember to rate.