When the microphone of your headset does not appear to be functioning correctly it is recommend that you check to ensure that the microphone is actually selected as the input device. NOTE: Usually this is done within the settings of the device you are connected to. For example on a PC you would go into the "Control Panel" and into "Audio Devices/Settings" (or something similar) and select the headset as the play back and/or communication device.
It is also recommend that you check the microphone input sensitivity to ensure it is set appropriately. If the input sensitivity is too low then the device you are connected to may have trouble detecting the microphone which could be interpreted as the microphone not functioning. If the input sensitivity is too high then the microphone could be overloaded and hence could be providing poor audio which could be interpreted as the microphone being faulty. NOTE: These adjustments are done on the device you are connected to NOT the headset itself.
Sometimes another peripheral device (like a webcam) will have a built in microphone and when this other peripheral device is also connected to the main device (ie: computer) then this built in microphone will automatically activate and become the default microphone (ie: overriding a microphone on a headset). You can check this by muting the headset microphone which would stop all sound through the headset microphone. If you are still picking up audio that would indicate that the headset microphone is NOT the input device but in fact some other microphone (like a built in microphone) is actually being used. If this is the case you may need to manually turn off the other built in microphone to allow the headset microphone to become the input microphone.