After doing Software Update to take it from 10.4 to 10.4.9, the Mac went into the spinning-daisy-icon mode for a long time. I just walked away from it for an hour. The screen was blank when I got back to it, presumably in sleep mode. Clicking the space bar sounded familiar, like it was coming to life, but the screen remained black and the fan started running faster and faster and louder and louder until it was a scream! I held down the power button to shut it down.
Back on again, the first thing I did was look in the log:
Applications > Utilities > Console
It said mdimportserver crashed(?). Maybe it’s something to do with Spotlight Indexing.