System Shutdown and User Logout Freeze

Question

Recently my Powerbook 15" G4 (FW800) compute running 10.5.7 has been having issues with both shutting down and switching to a different user from the Finder Apple menu.
You can select "Shutdown" from the Apple Menu and the system appears to close all programs properly including the Finder but my desktop image still appears on the screen and I have to hold down the Power button for about 5-10 seconds to force the computer to turn off.
In addition, if I try to log out of the current user using the Apple menu to try to switch to my other one the system again appears to "hang" with just the desktop image on the screen.
Initially when either of these attempts are being done you can hear disk drive activity but the desktop image stays on the screen even after leaving the computer alone for 10 minutes or more.
I've tried resetting the Parameter Ram at startup and even went as far as trying to reset the PMU by holding down the Open Apple-Control-Shift & Power Button (Apple says to hold down Shift-Control-Option-Power though) and I thought that had fixed the issue but after another reboot the computer is back to just sitting there with the desktop picture on the screen after shutting down.
I've run the computer in "Verbose Mode" and when the computer properly shuts down you can see the desktop photo go away and the verbose mode come up on the screen for a moment before the computer completely shuts down. But recently, after selecting shutdown on the screen, the computer never makes it to the verbose screen meaning "something" is causing it to hang after it closes all the processes but before it gets a chance to get to the verbose screen and close up shop.
Does anyone know of a preference file I can delete or something else I can try to get this computer happy again? Other than the above listed problem the computer works completely fine.
Any suggestions or other people that have had similar experiences are appreciated, thanks!
Mike

Answer 1

Friend, I feel for you. I have the same problem on two PPC machines. I have watched posts about this problem for about a year now, and I have yet to see anyone come close to a fix.
I'm going to tell you how we keep it from happening 97% of the time (on both our machines). It's really weird, but it works. When we're going to shut down, we open a few folders and let the machine calculate the sizes of the items inside. We use the Applications folder and the Utilities folder for this. Once the machine has shown the sizes of the items in the window, we close the window. Then, from the Apple Menu, we choose Shut Down (or Restart, if that's what we're doing). The dialogue window appears, asking to confirm that is what we want to do. Now, WAIT as it counts down. Click "OK" when the countdown hits 55 seconds remaining. I know it sounds goofy, but believe me, it works. If we do not follow this routine, the shutdown or restart will fail and we have to force quit the machine.
Now, we've been doing this for a long time - probably about a year. Since we started having to follow this silliness, we have installed a second hard drive in the desktop machine and also now use a portable FW HD with my laptop. On the laptop, I always eject the external HD before shutdown or restart. On the desktop machine, we simply open at least one big folder (usually Applications on a clone backup partition, and on the other partition just some big folder), let it calculate the sizes of the enclosed items, then close those folders. Following these actions, we use the previously described procedure.
Try it and let me know here if it works for you.
I know it sounds totally insane, but it works. It's a pain to do it every time, but it beats a forced shutdown and the chance of data corruption. I've given up on a solution; we'll probably replace these machines before there's a fix - judging from the lack of success other have with this problem.