The message "The Audio Service is not running" shows up as a red X on the speaker icon, and the audio troubleshooter sometimes reports it as "One or more audio service isn't running". Windows plays sound through the Windows Audio service, so when that service stops, every output device goes silent at once, even though the drivers are fine.
Fix it, in order
Restart the Windows Audio service. Press Win + R, type services.msc, and press Enter. Find Windows Audio in the list, right-click it, and select Restart. If it is stopped, select Start.
Restart Windows Audio Endpoint Builder too. In the same Services window, right-click Windows Audio Endpoint Builder and select Restart. Windows Audio depends on this service, so restarting only one of them often fails.
Check the services are set to Automatic. Double-click Windows Audio and make sure Startup type is Automatic, then do the same for Windows Audio Endpoint Builder. A service set to Manual or Disabled will not start with Windows.
Check the dependency services. Windows Audio also depends on Remote Procedure Call (RPC) and the Multimedia Class Scheduler. In Services, confirm Remote Procedure Call is Running and set to Automatic, since a stopped RPC stops audio with it.
Run the audio troubleshooter. Open Settings, System, Troubleshoot, Other troubleshooters, and select Run next to Audio. The troubleshooter can restart the services itself and will report exactly which service failed if the manual restart did not hold.
Restart the PC. A full restart reloads the service and its driver stack together. Test the sound immediately after the restart, before opening other apps.
Reinstall the audio driver. If the service stops again after a restart, the driver is the likely cause. In Device Manager, expand Sound, video and game controllers, right-click the audio device, select Uninstall device, and restart so Windows reinstalls it.
Check for corrupted system files. Open Command Prompt as administrator and run sfc /scannow, then restart. Damaged system files can prevent the audio service from starting at all.
Never set Windows Audio to Disabled to save resources, and be wary of system cleaning tools that stop services. The audio service has to be running for any sound device to work, and disabling it silences the whole PC.
If it still happens
If the service starts and then stops again within minutes, something is killing it. Check for a recent driver update and roll it back, run a malware scan, and look in Event Viewer under Windows Logs, System, for errors from the Service Control Manager naming the audio service. A service that will not start even after a driver reinstall and sfc /scannow points to deeper system damage, and a Windows repair install is the next step.
Common questions
Why does the audio service keep stopping? The usual causes are a bad audio driver update, a conflicting app that grabs the audio device, or a dependency service that failed. A driver reinstall and a check of the dependency services cover the first two.
The troubleshooter says the service is not running but it looks running in Services. What now? Restart both Windows Audio and Windows Audio Endpoint Builder together, then run the troubleshooter again. The troubleshooter checks the live state, so a stale entry in the Services window can mislead you.
Can I just restart the service every time instead of fixing it? You can, but it will keep stopping, usually at the worst moment. The permanent fix is the driver reinstall or the dependency check, since a service that stops on its own has an underlying cause.