macbook HD not booting. trying to bring up internal HD on another MAC, via firewire cable and holding down Command+Option+P+R for three boot chimes, the letting go.... does nothing, the apple boot screen comes up, and it turns off after a minute, as usual.

doing this correctly? my powerbook g4 12 inch is on, firewire cable connected. press power button on macbook (white), and the holding down the Command+Option+P+R button set to try to get into the firewire screen... is this correct? any help, please?!? thanks!