Read the detailed section of this article for step-by-step instructions on regaining access to your root account.

Here are the steps to retrieve access to root:

1. Click Restart at the login window

2. While the computer is restarting, hold down “Command-S” until you see text scrolling through the window. This boots the computer into single user mode.

3. At the Localhost% prompt type:

/sbin/mount -uw /

/sbin/SystemStarter

You will then see various services starting up.

4. When the Localhost% prompt reappears, type:

passwd root

It will then ask you to type the new root password twice, so do so.

5. After entering the new password, type:

reboot

At the login window, enter username root wih the new password. Once you are connected, you can use the Multiple Users application (/Applications/Utilities) to change your normal user’s password, or create a new user account.

Source: http://www.macpassword.com/recovering-lo...