Try an SMU reset:
Resetting the SMU on a G5 iMac:
and on resetting the PMU on a Power Mac G5, G4 and G3 :
Might as well try these resets if the above reset does not work.
ometimes if volumes don't appear in Startup Manager (what you get when you hold down the Option key at startup), you need to reset the Mac's PRAM, NVRAM, and Open Firmware. Shut down the Mac, then power it up, and before the screen lights up, quickly hold down the Command, Option, P, and R keys, until the Mac has chimed twice more after the powerup chime.
Then, before the screen lights up, hold down Command-Option-O-F until the Open Firmware screen appears. Then enter these lines, pressing Return after each one:
"The reset-all command should restart your Mac. If so, you have successfully reset the Open Firmware settings."
Should the fail...
Try taking the battery out for 10 minutes. Put battery back in. Cross fingers. Power the machine back on.
How to eject a cd from the internal cd drive:
List of devices:
List of variables:
More than you ever wanted to know about open firmware