On my dual 1GHz Power Mac G4 some, but not all, CD's will not open. I can hear it "spinning" but the sound is different from those CD's that will open. These same CD's that will not open on the G4, will open on an old iMac so it isn't the CD's. It sounds like a hardware problem to me, but the wierd thing about this is that I didn't seem to have this problem prior to my upgrade to 10.3.6. The CD/DVD drive is the Pioneer DVD-RW DVR-104.