Computer locked unable to log on with my password.

Is your shift lock on?

From Yahoo.

This message is seen when an attempt to login has failed multiple time. As a security measure, your account has been locked to prevent unauthorized users from being able to log in to it. If you have not recently tried to log in, this is not necessarily a cause for concern. Another Yahoo! user may have mistakenly used your ID when attempting to log in to their own account.
The lock on your account will expire 24 hours after it was first locked. Don't worry-the lockout time period won't reset each time you try to sign in while the account is still locked. You can try to sign in again after the lockout time has expired. Note: Yahoo! is unable to provide you with the exact time that your account was locked or when it will be unlocked.
If you are still unable to sign in with your new password, please see the password problems help page for some common reasons why you are seeing the "Invalid Password" error.

Typically the login problems are because of incorrect password:

1. Make sure that your caps lock key is turned off, then try to log in again.
2. If you were unable to log in after making sure your caps lock key was off, then try resetting your password by clicking the link reset password.
3. If you were unable to log in after resetting your password, follow these instructions to troubleshoot the problem. Reset your password once more here.
4. If you still can't log in, try using a different web browser.
   • If you do not currently have Microsoft Internet Explorer and would like to download it, please click here.
   • If you do not currently have Mozilla Firefox and would like to download it, please clickhere.
   • If you do not currently have Apple Safari and would like to download it, please clickhere.

1. Make sure that your caps lock key is turned off, then try to log in again.
2. If you were unable to log in after making sure your caps lock key was off, then try resetting your password by clicking the link reset password.
3. If you were unable to log in after resetting your password, follow these instructions to troubleshoot the problem. Reset your password once more here.
4. If you still can't log in, try using a different web browser.
   • If you do not currently have Microsoft Internet Explorer and would like to download it, please click here.
   • If you do not currently have Mozilla Firefox and would like to download it, please click here.
   • If you do not currently have Apple Safari and would like to download it, please click here.

1. Make sure that your caps lock key is turned off, then try to log in again.
2. If you were unable to log in after making sure your caps lock key was off, then try resetting your password here.
3. If you were unable to log in after resetting your password, follow these instructions to troubleshoot the problem. Reset your password once more here.

Password recovery tools are software tools designed to guess your password. Many of them work by making super-fast guess after guess until the password is discovered. They can sometimes be difficult to use but if you really need in and there's no hope of remembering the password

http://pcsupport.about.com/od/toolsofthetrade/tp/passrecovery.htm

start up you computer in safe mode and log on to the extra administrative account given. go to user account controls and delete the password for the other account (in safe mode you do not need to know what the password is you can just delete it). log back on and reset you password

the NUMLOCK key is to the right of the F12 Key on the top of the keyboard

You don't say what operating system you're using, but on the premise you're running one of the three last versions:
http://support.apple.com/kb/HT1274

The password can be reset by booting from your OS X installer CD and choosing “Reset Password” from the Installer Menu.

Here a link to the Apple website that details how to do this. 
http://support.apple.com/kb/HT1274