PowerMac G4 won't start up

You might want to check the pram battery on the motherboard if it hasn't been changed in a few years?

Troubleshooting: My computer won't turn on

http://support.apple.com/kb/TS1367

Some things to try.

* Reset the PMU http://support.apple.com/kb/ht1939

* Resetting the Logic Board - Resetting the logic board can resolve many system problems. Whenever you have a unit that fails to power up, you should follow this procedure before replacing any modules.

1 Unplug the computer.

2 Press the Power On button on the front of the unit.

3 Open the side access panel.

4 Remove the battery from the logic board.

5 Wait at least 10 minutes before replacing the battery.

6 Make sure the battery is installed in the correct +/-

direction.

7 Reassemble the computer and test the unit.

Note:

This procedure resets the computer’s PRAM. Be sure to

check the computer’s time/date and other system parameter settings

* Resolve startup issues and perform disk maintenance with Disk Utility and fsck

http://docs.info.apple.com/article.html?artnum=106214

* Your Mac won't start up in Mac OS X (Mac OS X 10.3.9 or earlier)

http://docs.info.apple.com/article.html?artnum=106464

* Troubleshooting: My computer won't turn on

http://docs.info.apple.com/article.html?artnum=300552

* Power Mac G4: Computer Does Not Power On, No Fan Movement

http://docs.info.apple.com/article.html?artnum=95038

Your internal PRAM battery may be weak or discharged. Suggest you replace the battery. Check this site for battery part numbers and sources. https://sites.google.com/site/macpram/mac-pram-nvram-cuda-pmu-battery-tutorialMac PRAM, NVRAM, CUDA/PMU & Battery Tutorial

 Cheers, Tom 😉