You might try this:
http://docs.info.apple.com/article.html?artnum=300832
Some audio applications may change your computer's audio settings to a sample rate that is too high for other applications to use. In this situation, system alert sounds still work, and does iTunes, but other applications may have no sound (audio output). This document applies to Mac OS X 10.3 or later and applications that use QuickTime 6 or later for audio, such as Safari and Quicktime Player.
This can happen on Macs that support high sample rates (higher than 48000 Hz):
iMac G5
Mac mini (all models)
Power Mac G5 models that support sample rates higher than 48000 Hz
PowerBook G4 support sample rates higher than 48000 Hz
MacBook
MacBook Pro
iMac (Early 2006) and later
Mac Pro
For example, if you play an Internet movie in Safari, it will make no sound; if you open a QuickTime movie on your computer, QuickTime Player reports the following error (and the movie will have no audio):
"You may experience problems playing a sound track in (Movie Name).mov because a software component needed by the movie could not be opened."
Solution
Open Audio MIDI Setup (/Applications/Utilities/), then check the Audio Output setting.
Change the Audio Output setting to 44100.0 Hz.
Quit Audio MIDI Setup.
Why does this happen?
Some third-party audio applications may change your computer's audio output setting. In fact, if you use the third-party application again after applying the above solution, the issue might occur again. Observe changes by watching the settings in Audio MIDI Setup before and after running a third-party application you suspect might be causing the issue. Contact the manufacturer of the application for more information.
