I recently formatted and reinstall Leopard. I also used Time Machine to restore my files. Everything is fine except that my microphone does not work. I checked it in System Preferences if the volume was down but it just doesn't seem to work. I'm using a PowerBook G4. Could be that a file is missing?
Open Audio Midi Setup in Applications>Utilities, see the input & output options & KHz setting there, some things will change it for their own use, then not set it back.