My G5 went ape yesterday. [2GB Dual; Model PowerMac 11,2 purchased 1/06)]
I googled "G5 Won't Eject CD". Got many hits so evidently it's a common problem. Thought I'd share solution suggested by Apple phone Rep.
Symptoms -- Would not eject CDs using keyboard eject button. Wouldn't show CDs in sidebar, etc. Also...G5 icon in sidebar turned generic. Also...at or about same time, "system failure" msg appeared on desktop and fans spun loudly. Ran Disk Utility from OSX disk. Did verify and repair -- there were some repairs listed which Disk Utility successfully fixed.
How to eject -- various ways: Restart while holding down mouse button worked for me
How to prevent -- Apple rep said do an Archive and Install from OS X disk.
Results -- Did the "A and I". Inserted 1st CD. Nothing happened till I rapped knuckles on front of CD hatch. Works fine so far...knock on wood. Fixed G5 icon.