Macintosh question (G3, 7 years old, so OT)

A quick question about the Mac G3, if you'll forgive it being not yet on-topic. Feel free to reply off-list to avoid rampant topic drift... Does anyone here know about the internals of the G3 line? I have a motherboard in front of me that I'm attempting to see if it will work. It came from a machine that had already been stripped, so there's no guarantee the hardware is functional. With the Apple Reset/NMI board installed, and RAM, and the Apple-enhanced ATI Rage 128 video card, I've attempted to see if it works by plugging in a PC ATX power supply and pressing the "power on" button on the motherboard and on the Reset/NMI board. I get a brief green flash from several LEDs, but the PSU doesn't kick on the fan, and the machine does not appear to be starting. Do I need an Apple ATX supply to test this? Could this be a battery problem? (the battery was completely dead and I have no handy replacement, so the battery compartment is empty) Do I need to have a keyboard and mouse plugged in to get a response?