No sound

[Robert Raposo]

  After downloading iTunes 4.5 my sound output has gotten squirrly.
  I noticed this first after using iTunes, then stoped the player for a 
while, when I returned, no sound.
  After restarting, I have sound for a while, then it disappears, I 
check the settings in the "Sound" System Preferences, they are OK, then 
when I move the output volume slider from right to left to right and 
check an alert sound, I have some weak output. then silence. Did the 
same in Audio Midi Setup. Restart: no startup tone. I ran Tech Tools 
Pro 4.1 last night and there was a startup tone when starting from the 
CD. Ran the tools, repaired minor problems. This morning had a startup 
tone, just opened iTunes; no sound.
  I will copy the System Log next time and post it.
  Let's get this fixed!!
  I use Logic Pro and this is a disaster.

There is a thread on Apple Discussions:
PowerBook  > PowerBook G4 17-inch  > Usage > no sound