[G4] Upgraded to 10.4.10 and now it won't shut down

[JayB]

Hey gang-

I needed to install my upgrade to CS3 (photoshop) so I had to jump  
from Tiger 10.4.1  at least 10.4.6.  I went ahead and downloaded and  
installed the upgrade to 10.4.10.

Although CS3 runs (slowly), and everything else seems OK, the CPU  
won't do a proper SHUTDOWN.  It empties the screen down to desktop  
color only and hangs.  No wheel (curser fine), no other clues.

I've since zapped the PRAM, and run Disk Warrior 4.

No Joy.

I've got a 500 AGP boosted to 1gig  (and a gig of RAM) that has run  
smooth for 5 yrs.

Until now, things were fine.

Clues?