I just started using Skype and use a Plantronics USB headset/microphone. It works pretty well calling a phone but has a really annoying side tone when calling another computer. My problem, though, is that since I started using the headset, just a few days ago, my built in microphone and speaker and the ability to plug in just a headset and listen have vanished. Also, the volume icon in the menu bar has disappeared. If I go to System preferences, there is only plantronics in the menu. I've tried restarting with no change. It used to work just fine...where might it have gone?