If you forgot your password, request a new one.
For more information regarding Yahoo! IDs and passwords, please read this help section.
There are several reasons you may be getting the "Invalid Password" error message:
Set your CAPS LOCK key correctly. Passwords are case sensitive, (meaning that "PASSWORD," "PaSsWoRd," and "password" are not equivalent), so be sure to keep this in mind when entering your password.
Wait up to 24 hours. If you recently requested a new password, this will allow your account to update.
Delete your cookie files. A cookie is a small piece of information stored by your browser that helps identify you. If your cookie is not being accepted correctly, you will be logged out of your account as soon as you move to a different page. This may be blocking your current ability to log in or stay logged in.
To delete your cookies, close all browser windows, find the "cookies" directory, and delete the cookie files inside. As always, make sure that you have selected the proper files before deleting.
If you're still having problems, please request a new password. Once you receive your new password, you can change it.