black screen of death and kernel panics

I recently bought a new iBook G4 to replace my iBook G3. Over the past week, and after about 3 weeks of normal use that has been uneventful, I've suffered several kernel panics quite unpredictably. In the worst case, the Finder would always freeze on startup, and I had to do an archive and install of 10.4.2 to get back to a working iBook. Today, just 3 days after the archive and install, I've tried to wake the iBook after putting it to sleep using the command (rather than just closing the lid), and found myself with a black screen of death (num lock works, sleep light goes off, but computer is otherwise a zombie) and had to remove the battery to force a hard shutdown in order to restart. I ran /etc/weekly and /etc/daily to do the corresponding maintenance tasks, since someone reported success in a similar situation after that. But after doing that, I went to shut the machine down and it went into another kernel panic.

Ideas and suggestions are welcome. I'm about to try resetting the PMU to see if that is helpful. Weird that this is happening after 3 weeks or more of normal usage, and after doing an archive and install of the OS.