Although I have already answered this Q, I am just pasting the same thing again, as my user id is not working, the old one:. I will just edit the other answer of mine...
There are certain reasons & certain remedies:
1.Your account has been locked for security reasons, this means that there have been too many attempts to sign in to ur account with the incorrect password. As a security measure, ur account has been locked to prevent unauthorized users from being able to access it.
If u haven't been trying to sign in to ur account with the wrong password, this is not necessarily cause for concern. It could simply be the result of another user mistakenly thinking that ur ID is theirs. (To learn more about account security, visit the Yahoo! Security Center.) http://security.yahoo.com/
1.This usually happens when an incorrect password is repeatedly used, and is for security reasons. Lock out is in force for 24 hours - you will have to wait it out.
2.Visit this link, & gives you the complete details of how to go about it: http://help.yahoo.com/l/us/yahoo/edit/id_password/edit-22.html
Yahoo! uses temporary, automatic account locking as a security measure to protect accounts from unauthorized access. Sometimes you can also become temporarily locked out of your own account as a result. If you (or someone else) uses the wrong password three or more times when attempting to sign in to your account, the account is locked, for your protection, for 24 hours.
Reasons you might see the message: "Account locked for security reasons" when attempting to sign in:
•Three or more failed sign in attempts: This triggers our security system to temporarily lock the account for 24 hours. •Someone with a similar Yahoo! ID accidentally typed your ID on log in: If you haven't recently tried to sign in to your account, then it could be someone else's harmless mistake. Their Yahoo! ID may be similar to yours and they may have mistakenly typed in your Yahoo! ID instead of their own. •Automatic security measures: In case an unauthorized person tried to access your account, we lock it for your protection.
How our account lock works:
•It lasts 24 hours, starting on the third unsuccessful log in attempt. •It doesn't reset. Attempting to login again within the 24 period will not help. •Try again after 24 hours. Once the lockout time has expired, your password should work as usual. •We can't provide the lock time information to you. We can't give you the exact time that your account was locked or when it will be unlocked.
•If you see an "Invalid Password" error message, see our help article about how to recover a lost password or go directly to our password helper. •If you think someone may have accessed your account, see our help article on compromised accounts."