I had an interesting one today. A lady phoned in Brisbane needing help with her Apple Mac. She was unable to turn off parental controls which had unknowingly been activated on her account. She wasn't an admin user on her Mac, and we found there were no other admin users on the Mac to allow us to make her an admin... but how is that possible?
Anyways... rather than worry about why it happened we worked on how to fix it.
Barbara was running Mac OS X 10.8. I had her reboot the macintosh and start up in Recovery Mode by holding ALT/OPTION, then choosing the Recovery partition.
When we arrived in Recovery Mode, I got her to choose "Utilities" from the menu, then "Terminal." We entered "resetpassword." This brings up a window. In this window you choose "Macintosh HD" or the name of your main hard disk. We reset the password for the "root" user. After rebooting we were able to login as "Other" user, and enter "root" and the password that we set.
This allowed us to enter "Users and Computers", then choose her original account and make her an administrator. While we were there we turned off Parental Controls.
Voila! done... Another happy user....