Hello;
Have you tried to reset the PMU button? It is located on the logic board just above the battery.Press and hold for a couple of seconds,while the machine is off,then try to restart.If nothing happens read the following,it is from the apple service manual for G4 Macs
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1 Power Macintosh G4 (PCI Graphics): Check LEDS DS7 and DS8 on the logic board. In a working unit, these LEDs should be in sync with each other: both on or both off. If one LED is on and the other is off, there is a problem.
2 Verify power outlet is good. Try a known-good power cord. 3 Make sure the voltage switch on the back of the power supply
is set to the correct voltage. 4 Check for trickle voltage on the power supply connector.
Refer to “Power Supply Verification” in this chapter. 5 Disconnect the keyboard and power-on the system via the
power button on the front of the computer. If the unit powers
on, replace the USB keyboard. If not, go to next step. 6 Power Macintosh G4 (PCI Graphics): Reset the Cuda chip and
try again. See “Resetting the Cuda Chip” in this chapter. 7 Reset the logic board:
To test the power supply,you will need a digital voltmeter.Do the following;with the machine off,remove the power supply connector from the logic board.The connector should have 22 pins.Turn the machine back on.Looking at the connector from the board side,you should have the alignment bump to your right.Turn on your meter and insert the negative probe into pin# 11,upper left corner,positive probe goes to pin#22,on the upper right corner,you should have 25 volts or better on a Quicksilver.If not you need a new power supply.
You might want to keep in mind that the replacement mother board might also be bad.
Hope this helps!
