WARNING: I will not be held responsible for anything you do to your computer. Please follow any of the below instructions at your own risk. Be sure to always follow Apple DIY Hardware Replacement instructions (you can download these for any model in pdf format), use official Apple parts, and use anti-static discharge kits and the proper tools, do not steal or commit adultary (on purpose), make sure to feed your pets, and love Our Beloved Leader Barack Obama with all your hearts, minds, and souls.
ON TO THE BUSINESS!
I know everyone is just hungering for this solution, especially since Intel Macs after a certain date do not even use Open Firmware (they use a firmware protection called Extensible Firmware Interface (EFI) technology)… however, for those 3 of you who have picked up old PPC macs that you desperately want to defile and warp to your nefarious purposes, but cannot because of open firmware restrictions (not letting you netboot, or boot from CD, or use any sort of keyboard boot options), even with the old ” remove the RAM and reset PRAM” trick, this post may be just what you are looking for!
CASE: iMac G5 (flat panel) has open firmware that does not allow keyboard boot commands. Additionally, the machine is set to Net Boot, so at boot, there is blue globe, followed by a sad folder with a question mark (“where’s my net boot friend” it screams!)
OLD SOLUTION: Open Firmware can usually be reset by removing a stick of RAM and resetting the PRAM: remove the RAM (after unplugging the machine!), close all bits up again, and start the machine – at the chime, hold down apple(command)+option+p+r. You will hear another chime – hold for three total chimes, then let the thing go. This will reset the open firmware password, effectively removing the password protection.
This can sometimes fail, however, as it did for me in the case above. I cannot say exactly why, but the following DID remove the password protection.
SOLUTION: remove ALL RAM from the machine. In this case, the iMac G5 has parallel RAM slots, both easily accessible and both accepting the same RAM quantities. I first started the machine, let it try to netboot,and stuck in my official Leopard Install DVD (purchased from Apple :D) which it gladly accepted. I then powered off the machine. I unplugged it, removed both RAM sticks, popped the back on, and started her up. Instead of hearing the usual happy apple startup chime that we all love, a heard a frantic and death-signalling beep. Having no RAM at all makes for sad macs! No key combos work, no graphic interface, nothing: a Formless Void… So I unplugged the machine, popped the RAM back in (swapping the two sticks which were botht the same kind — 512 ), plugged and powered it on. Upon hearing the chime (return joyous happy chime!), I held down the PRAM reset command above (apple(command)+option+p+r), for two chimes. Immediately after the second chime, I released the PRAM reset keys and held down c to boot from CD (in this case, DVD) and viole, triomphe!
With some models you may not be able to get at all of the RAM: such is the case with the snoball, for example. Try the above removing all the RAM you can. In a worst-case scenario, all solutions will fail, and to boot (sorry!) your disc is stuck in the machine and hitting eject will not spit it out… :'( Hold the mouse button on startup to eject the disc… at least you have that back now!
If you have other solutions that worked for you, post ’em below!