Q: I dont know my administrators name and password for my G5 iMac. I have tried t change it using my install disk but it didn't work. Said there was some kind of failure? I don't think I have ever known the password? I had apple care when I first purchased.

We need to know the exact error.  Please try again.

You may want to run these "standard" fixes if the problem persists.

1) Check the amount of free space on your harddrive.  You should have a several gigs free.

2) You should run disk utility

      Macintosh-HD -> Applications -> Utilities -> Disk Utility

      a) verify the disk

      b) update your permissions.

3) Try a safe boot.

     Shutdown your machine.  Hold down the shift key.  Poweron.  Wait awhile Wait awhile while you harddrive

       is being checked.

     http://support.apple.com/kb/ht1455

I bought a used Mac and didn't know the administrator's password. However, since it was already scrubbed and erased by the previous owner I had no data to lose. I think I just erased everything again and reinstalled Snow Leopard. That allowed me to put in a new administrators password.