ITunes causing whole system to freeze?

Question

Hi
There are a lot of questions on this forum which are similar to this, but I have not found one that actually replicates the same problem in the same conditions.
Today I was listening to iTunes and had a bunch of other applications open. For no apparent reason, the whole system froze up on me. By this I mean: the mouse no longer responds, keyboard no longer responds, the colon that flashes the seconds in the clock stops flashing (I have that turned on so that I can see when the machine is really frozen), and all the keyboard-shortcuts like Option-Command-Esc (Forced Quit dialog) or Ctrl-Eject fail to work. Even the Ctrl-Command-Power doesn't work (for forced Restart): instead I have to hold the power button for a few seconds and the computer shuts down, but does not restart. (This is what I mean by the 'whole system freezing'). There is no warning, no beachball spinning, and the G5 does not even seem particularly hot (the fans were not blowing hard). So I am completely at a loss to understand what's going on.
Thinking this was a one-off event, I restarted, ran a "Verify permissions" and "Repair permissions" (was this a mistake?) and ran a few applications (Mail, Safari) all of which worked fine. Then I opened iTunes again. It opened OK. I then closed the window, which worked. Then I quit iTunes. This caused the whole system to freeze again, exactly as before.
I have repeated this cycle a couple of times. iTunes will open, will even start playing a song, but on Quit the whole system freezes.
More recently I found that the system froze with iTunes just playing a song.
What then happened was that I looked for help on this forum, found too many cases of iTunes doing strange things but none with my configuration, and thought (perhaps recklessly) that I should update iTunes (from 6.0.4 to 6.0.5). This seemed to work perfectly. Except when I opened it, and played a song, within seconds the whole freezing thing happened again, exactly as before.
So, apart from giving up on listening to music in the office, what is to be done? I am able to run other applications OK (I'm writing this within Safari), so it seems to be an iTunes related problem. I had no unusual devices connected (in fact nothing except keyboard, mouse, monitor), and no iPod connected.
Does anyone know what to do about this?
(I'm using a Power-PC based dual G5 which is only about 15 months old).
Thanks in advance.
PowerMac G5 Dual 1.8GHz, PowerBook G4 12" 1.33GHz   Mac OS X (10.4.5)  
PowerMac G5 Dual 1.8GHz, PowerBook G4 12" 1.33GHz   Mac OS X (10.4.5)  

Answer 1

Just an update (I'm answering my own post) in case anyone else has this issue:
I managed to get iTunes to stop causing hard crashes. I went through the repair disk procedure outlined here:
http://www.thexlab.com/faqs/repairprocess.html
Including running Yasu at the end with most of the boxes ticked, to clean caches thoroughly.
And I also trashed all the iTunes preferences files. The first time you run iTunes after this you have to answer some questions (as it resets the prefs) but you can always restore your settings manually afterwards.
So far so good -- iTunes launches, runs, and quits without crashing the system.
I guess this might not have been an issue with iTunes itself. The damage was probably done when the first crash happened and I had to use the power button to shut down. I still don't understand what caused the first crash, though, and Yasu seems to have deleted the panic log so I'll never know.
PowerMac G5 Dual 1.8GHz (1 GB RAM), PowerBook G4 12" 1.33GHz (768 MB RAM)   Mac OS X (10.4.5)