In case you have faced this issue on MacOS, please check this article.

Please check whether the issue is in the program preview or it reproduces only on the output. 

If the issue is in the program preview, check whether your sound device is active. 

If you cannot enable sound from any device please follow this guide

When the problem comes up only at the output file, there are several options to try: 

1) If you hear the audio on the program preview, try saving  the video using another codec. 

Click the menu 'Save as' in the preview, click the cogwheel icon (codec settings) next to the format option and select the MP3 audio codec.

To open a recently captured file, select the option Capture - Open recorded file.  

If you save a video for a specific device, please check its supported formats for a better compatibility. 

2) You can use a different media player. 

The file does not play on a default player? 

It is possible to use the one that does not use the system codecs. 

For example, one can try an opensource GOM player or VLC player

3) You can install codec pack to make your PC play that video or audio file. 

An example of a complete codec pack is KLite codec pack

4) If you are using a specific device for recording, try disabling all other active devices, or try choosing these devices in the dropdown menu next to microphone icon.