Start your MBAIR in recovery mode. and from the status bar go terminal.
Type: resetpassword
it will open you a second window. from the top select your harddisk and you will be able to see users in the hardisk if you misstype it you can correct it.
as a further step; select Root user put a password foe it and restart. log in with Root user and repair everything in the other user from system preferences > users and groups
When you finish the tasks that require logging in as the root user, always log out, log in as an administrator, then disable the root user.
- Open Users & Groups preferences, click Login Options, then click the lock icon to unlock it. If necessary, type your password, then click Unlock.
- In the Network Account Server section, click Join or Edit.
- Click Open Directory Utility.
- Click the lock icon to unlock it, then enter your administrator name and password.
- Do one of the following:
- Choose Edit > Enable Root User, then enter a root user password in the Password and Verify fields.
- Choose Edit > Disable Root User.