When you change your Yahoo! account password, the password that the Yahoo! Messenger application automatically enters for your in the sign-in window is not your new password. This is true even if you have set Yahoo! Messenger to remember your ID and password. When you change your account password at Yahoo!, you must separately update the Yahoo! Messenger application on your desktop or mobile device with your new password.

Here's how update Yahoo! Messenger with your new password:

1. Open Yahoo! Messenger.
   
   
2. In the main Yahoo! Messenger window, clear out your Yahoo! ID by selecting your Yahoo! ID in the Yahoo! ID text box, and then press Delete on your keyboard.
3. Re-enter your Yahoo! ID by typing it in the Yahoo! ID text box.
4. Clear out your old password by selecting your old password in the Password text box and then press Delete on your keyboard.
5. Enter your new password in the Password text box. Leave the Remember my ID checkbox selected, if you wish.
6. Click Sign In.

To protect your account, Yahoo! sets a limit on the number of unsuccessful sign-in attempts allowed in a set period of time. If that limit is reached, Yahoo! sends a security message to the account owner stating that the account has been locked for security reasons. This lockout expires after 24 hours. If you have accidentally tried to sign in to Yahoo! Messenger with your old password, wait a few minutes before going through the sign in process again with your new password to avoid this lockout situation.