Computer USB Headset Troubleshooting: No Transmit on Mac 10.4.10
USB Headsets: No Transmit on Mac 10.4.10
The following applies only to Macintosh computers running Mac OS X 10.4.10.
If you experience no transmit (i.e. the mic doesn't seem to work), please try the following:
Make sure your Plantronics microphone is plugged into an open USB port on your computer.
Launch "Audio MIDI Setup.app." (You will find this application in Applications> Utilities.)
In System Settings, select "Plantronics Headset" as the default input.
In "Properties For:" select "Plantronics Headset."
In the bottom right area of the window, uncheck "Mute."