I had a little scare this evening. At work, I ran Software Update to install Mac OS 10.4.8. When it finished, I clicked on the Shutdown button. When I got home, I attempted to boot my PowerBook. The computer didn't play the chime, and the screen didn't turn on. This continued even after plugging in external power and removing and inserting the battery.
I went to the Apple Store to see how much it would be to fix it. I though that the problem was with the motherboard. I wanted to find out if fixing the PowerBook would be more than getting the 2.16 GHz MacBook Pro (wouldn't that be a shame).
When I got to the Apple Store, and finally got seen at the Genius Bar, my PowerBook started up. The person at the desk mentioned that the 10.4.8 upgrade actually reboots the computer twice, so I probably wasn't letting the first boot finished (I don't know why the chime was disabled for the first boot.)