Does your Mac's sound volume setting mysteriously get moved to the maximum setting? The problem may be After Dark. According to reader Tim Schemmel, Berkeley Systems confirms this but did not say when a fix would be available.
Meanwhile, I continue to get email from readers complaining that their volume level gets mysteriously reset to mute. I have covered this issue before. There are many possible causes and solutions. For starters, try deleting the Sound Preferences file. Also, if you use Energy Saver, make sure its "Mute Sounds while the computer is asleep" option is not checked. Stephen Arnold claimed that there is a potential conflict between OpenTransportLib and FreePPP that can result in the loss of sound (although I cannot confirm this).
Finally, you can try the Unmute-it utility here in the Download Library. It is possible that none of these solutions will work, especially with some Performa models, but this should solve most problems.