System loses sound when a display is connected using a DisplayPort or High Definition Media Interface (HDMI).
When an audio-supported video cable is being used such as a DisplayPort or HDMI cable, Windows may change the default audio device to the audio-supported cable thinking another audio device is being used. The issue may be seen to occur when a portable is coming out of sleep as the system is detecting the audio-capable cable first.
Go into the audio playback devices settings (Start > Control Panel > Sound; or in Windows 10 go to Start > Control Panel > Hardware and Sound > Sound | Manage audio devices ) and change the default audio device back to the internal speakers/headphones.
The external audio device causing the issue can be disabled so issue does not occur again.
Additional Reference for Troubleshooting Sound or Audio Issues:
Article ID: SLN286116
Last Date Modified: 03/13/2019 04:28 PM
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