my audio volume control defaults to mute whenever I start the computer. Preference settings have no effect. Technical support couldn't help.

Thanks for the inquiry and feed-back. Tech support advised me to unlock the preference dialog box when I was logged in as the administrator. We changed the volume setting to mid-way on the scale and rebooted but the volume preferences reset to minimum volume with Mute ticked. He also had me try what I assume is a reset of defaults on boot-up. I held the Command/Option/P keys and operated the power on switch, then immediately held down the R key which put the computer through a different start up sequence. Once again the volume was muted and indicated minimum when I checked. No luck either when we created a New User account and set the volume control to mid-way as previously mentioned. Other approaches he suggested were too involved for me to accurately relate but involved deletion of some files associated with the sound system. No joy which is why I have sought other advice. Thanks anyway for your interest!