I've been using Windows 10 64-bit on my Dell Inspiron 3521 for an year now and suddenly I came to an issue yesterday. There is an red "x" near my sound icon and it just says no audio output device installed. I tried right clicking it to change the settings but it shows Speaker Setup : UNKNOWN. I guess this has happened because I've messed something in the drivers. But I tried to fix it by watching YouTube videos in which they provided a solution through uninstalling/updating drivers but it isn't working. Also nothing changed after restarting the audio services. Please someone kindly help me to fix it. Thanks for the time!
Thanks for posting. Apologies that your system is not performing as expected.
From your description, it appears that a recent Windows update may have caused this issue. Have you tried changing the restore point to one before the last update? Also, have you tried removing the Audio devices in the Device manager, then rebooting to reinstall the native audio drivers?
Have you tried plugging in headphones or external speakers? What happens then?
Here is information from the Dell knowledge base you may find helpful: