Old Mac OS X, cannot get admin access, boot safe or single-user mode, nor reinstall

I have inherited an old Mac OS X 10.5.8 + original install DVD.

• Model: Power Mac G4


• Identifier: PowerMac3,6


• Processor: PowerPC G4 (3.2)


• DVD: Mac OS X Leopard Install DVD Version 10.5

I'm trying to reinstall from scratch, including erasing all the existing data.

I have the username / password for a standard account, and can log in using this.

I cannot get the install DVD to run. I have tried numerous things including:

• Booting directly from disc ('C' key)


• Booting into safe mode (Shift key)


• Booting into Startup Manager (Option key)


• Booting into single-user mode (Cmd + 'S')


• 'su' and 'sudo' from a command-line terminal (user is not in the sudoer's list)


• Making various changes via 'System Preferences' (asks for admin account)

There appears to be only 1 account - the standard account I am logging in with. There appears to be no admin account of any kind.

The attempts to boot with the various keys depressed appears to have no effect whatsoever. The normal boot sequence runs. The DVD is ejected during this boot sequence.

Only holding down 'shift' prevents iTunes auto-running after login. (Which means the keyboard works, I guess!)

The only thing I haven't tried (I think) is to use an old Ubuntu CD (Disk Utility asks for admin account) to wipe the drives and see if we can force a boot from the install DVD that way. But that seems a bit drastic, and is permanent if it doesn't work.

Is there anything I haven't tried, in order to regain control of this Apple hardware?

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I have tried all of the solutions found at these questions: -

• MacBook Pro won't boot into safe mode or from DVD


• Constantly ejecting OS X install disc when trying to boot

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Update:

By physically unplugging and removing the hard drives, the computer is forced to boot from the installer DVD. Obviously at this point there is nothing to install onto, but it proves that both the DVD player, and the DVD do work.