Click the loudspeaker icon at the right end of the 'Task Bar', and then click the loudspeaker icon at the left end of the horizontal volume bar. If it is only F4 that no longer works, the workaround is to use software control to mute the sound.If it is not running on your system, right-click on it and select start. Check whether the service named 'hidserv' is running. Open the Windows Task Manager and switch to the services tab. How to fix volume keys not working on USB Keyboard in Windows 10.
