There is no known on/off setting. There is the control panel, sound and such but it sounds like you've been there.
I can play sounds OK - including the voice from a Skype partner - but the PC mike doesnt pick up my voice. I opened the control panel > audio link - no microphone-mute checkbox, & the mike-volume slider works. I tried the sound test: it confirms my voice doesnt record. I have no external mke. I havent used this PC for several years. The internal mike used to work fine. The Conexant audio-in driver is "working properly."
Any XP options to enable the internal mike?