Hi,
This will happen if the Microphone in the Computer is not enabled or if the Audio Driver is not installed correctly.
To make sure that you have enabled the Microphone in the computer, please right click on the Sound icon on the System Tray (right corner of the taskbar). Then, select the "Recording Devices" option. This will open the Sound Properties window. In the Speaker/Headphones Properties
window, click on the Levels tab. Then, on
the Levels tab, next to Microphone , click on the
speaker
button to enable the microphone.After that click
the OK button and close the open
windows. This will enable the Microphone in the Computer.
If the issue still persists, you may need to re-install the Audio Driver in the computer to fix it.
To download the Audio Driver for the Computer, click herePlease download the file to a temporary folder in the Computer. After that, please open the folder where the file is downloaded and double click on it to begin the installation. Please follow the onscreen instructions to complete the installation process. After that, restart the Computer for the settings to take the effect. Re-installing the Audio Driver also fixes the issue with the Microphone. Hope this helps..
Good luck..!