OS X Keychain will not unlock

If you can not unlock your keychain delete your keychain file from the Keychains folder located in the Library folder in your Home folder, then logout and back in again. This will recreate a keychain file for you with the correct password.

Your keychain is a file used by OS X to store your passwords for various services, allowing you once you have logged in and automaticaly unlocked your keychain to use email etc. without having to constantly re-enter passwords.