My G4 (dual 450, 640M, 4 hard drives) always used to go to sleep normally on timeout or when I touched the power button on the monitor. It still does when booted into OS 9.2.2. Now in OS X the screen goes black and the drives stop, but the processor fan keeps running and the power light stays bright rather than pulsing. Behaviour is identical no matter how sleep is requested -- timeout, or menu item, or power button.
This began a couple of weeks ago, with no obvious correlation with any system change. I had been running 10.2.6 for a long time. It continues in 10.2.8 (which has caused no obvious problems for me).
I assume that some application (native not Classic, since the problem occurs even when Classic has not been started) is preventing it from going to sleep. Can anyone suggest a good way to find the culprit?