Welcome to the Community.
As per our understanding it seems that the internal microphone and the internal speakers of the system are not functioning , please follow the given steps :
Request you to update the audio drivers form the following link: http://dell.to/LzfIrZ
Also check under the control panel, Sound and Audio setting the default device is not empty, if it is select the appropriate device.
Hopefully that will help you to get this issue resolved, however if it doesn't work would request you to reply with the following info.
Since how long have you been facing this problem?
Was there any update /new sotware that was installed on the system?
Is it only not working online or its not working even if you use any playback music and recording?
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