I'am having a problem nearly identical (PM9600/200 with Newertech Maxpowr G3/300-200 and a ATI radeon7000)
if possible bring your system up to OS 9.1
then shut down the PM9600, get de powercord ou, wait at least 5 min, push the startup bottom (decharging the residual electricic energy in your machine),
open your mac, use a special strap around your wrist connected to the metal parts of the mac - equipotential aginst static electricity (or if you don't have such thing touch the powersupply or other metal parts regualary when your work inside) get your battery out and push on the SCUDA button for 30seconds (those 30sec might drain your battery) - replace the battery (before test your battery - she should give at minimum 3.2Volts new = 3.6V - if to low replace), put everything back and ........ start the mac
good luck