If you lose your Yahoo email password, there are three basic methods for you to regain access to your Yahoo email account:

•Reset your Yahoo email password online
•Recover your Yahoo email password from your web browser
•Recover your stored Yahoo email password from the Windows Registry

Reset your Yahoo Email Password

The easiest way to recover a Yahoo email password is to go the the Yahoo! Sign-in Problems page. To use this page, first enter your Date of Birth, Zip Code, and Country to verify your identity. Next, enter your Yahoo Email ID and Yahoo will email your Yahoo password to the e-mail account associated with it. If you can not remember your Yahoo ID, enter the email address you used when you signed up for your Yahoo email account and Yahoo will send your Yahoo ID to that email account. If you no longer have access to the other email account associated with your Yahoo ID, Yahoo will refuse to assist you.

Recover your Yahoo Email Password from your Web Browser

Most Yahoo users allow their web browsers to store their Yahoo password. Every different web browser stores the Yahoo password in a different manner. The method for recovering these stored passwords is different for each web browser.

How Internet Explorer password recovery work?

Internet Explorer stores usernames and passwords for web sites which you have logged in to.
Internet Explorer stores these usernames and passwords in what is called Microsoft Protected Storage.
Password storage is configured in Internet Explorer under <Tools>, <Internet Options>, <Content>, <AutoComplete>:
 
Viewing Microsoft Protected Storage
Microsoft Protected Storage stores the usernames and passwords in a set of registry keys.
Several programs, with widely varying capabilities, are available to help you view Microsoft Protected Storage:
•   Protected Storage Explorer
•   pStoreReader
•   Elcomsoft Advanced Internet Explorer Password Recovery
•   Rixler Software Internet Explorer Password Revealer
•   SecretExplorer
•   IE Key

How Netscape Navigator password recovery work?

Netscape Navigator stores usernames and passwords for web sites which you have logged in to.
Password storage is configured in Netscape Navigator under <Edit>, <Preferences>, <Privacy and Security>, <Passwords>:
 
By default, Netscape Navigator stores all passwords unencrypted.
Viewing Netscape Navigator stored passwords
The usernames and passwords are stored are part of the Netscape Navigator user profile.
The location of the Netscape Navigator user profile varies between versions and installations.
My Netscape Navigator user profile is stored in C:\Documents and Settings\Will\Application Data\Mozilla\registry.dat.
Netscapass will help you view stored Netscape Navigator passwords:
•   Netscapass
Recovering Netscape Navigator encrypted passwords
I am not aware of any currently existing software to decrypt Netscape Navigator encrypted passwords.
Known weaknesses in the password encryption system of Netscape Mail lead me to believe that an application of this nature could be created, and simply has yet to be written.

Getting your Yahoo Email Password from the Windows Registry

If you are running Yahoo Messenger in addition to Yahoo Email, you can use Mail  PassView or Advanced Instant Messengers Password Recovery to retrieve your Yahoo password from the Windows registry.

If you are running Yahoo Pager, you can use Anti-Secure to retrieve your Yahoo password from the Windows registry.