Apparently there is a glitch with some Macs and the program Quicktime, which is an Apple product.
Some applications may output no audio, but system alert sounds and iTunes playback can be heard Summary With QuickTime 6, applications that use QuickTime for audio 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 and iTunes audio still work, but other applications may have no sound (audio output).
This problem can happen on Macs that support high sample rates (higher than 48000 Hz), including these:
MacBook (all models)
MacBook Pro (all models)
Mac Pro (all models)
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
iMac (Early 2006) and later
Some videos/movies will play the video but no audio. ‘
Perian enables Quicktime to play a variety of formats with both video and audio. But you need to have OS Tiger or later for it to work
http://www.perian.org/. I think you need to install perian ( which is a free program)] to hear audio on the above mac computers. Having an updated version of quicktime on your computer also might help.
Thanks again for all your support.