The headset may not be turned on or the headset may not be connected to a mobile phone. Press the call control button for 2 seconds until you hear a beep or see the indicator light glow blue to turn the headset on.
Your headset may be out of range. Move the headset closer to the phone or Bluetooth device.
Your headset battery may be drained. Charge your battery using the A/C power adaptor supplied.
The listening volume is too low. Press the volume key up (toward the earloop) to increase the sound heard in the headset.