Mac administrator account changing to a standard account

We have had several reports of Macs that have their admin account changed to a standard account.

The fix is to login to the machine as root, go to "Accounts", select the admin account and put a tick in "allow user to administer this computer".

If the root account is disabled or you do not know the password you will have to boot the machine from the OS DVD and enable the account/reset the root password.

Full instructions can be found here:

http://support.apple.com/kb/TS1278

Missing admin accounts on Mac: FIX

Shut down the computer if it is on.
Press the power button to start the computer.
Immediately press and hold the Command (Apple) key and the "s" key for single-user mode.
Type "mount -uw /" and press return.
Type "passwd" and press return.
 Enter new password (this will be for the root user account) and press return.
Type "reboot" and press return.
Enter Account settings and when prompted for administrator account and password, use the user name root and the password you just setup
Check box for you standard account to administrate box
 If all goes well you are admin again.

Then log in as Root:

dscl . -create /Groups/admin
dscl . -create /Groups/admin RealName Administrators
dscl . -create /Groups/admin PrimaryGroupID 80
dscl . -create /Groups/admin Password [password]
dscl . -create /Groups/admin GroupMembership root

Original post:  http://macosx.com/forums/howto-faqs/299801-howto-fix-user-lost-administrator-privileges.html