I managed to fix the issue by going to   and downloading any "urgent" driver updates such as the System BIOS as well as any keyboard or audio-related drivers. 
Hello, I have a Dell Latitude 7400 2-in-1 laptop and recently the "mute microphone" function on the f4 key has stopped working. Normally, when I press the f4 key, the white LED light indicator should toggle on and off to show whether the internal microphone has been muted or not. However, the "mute microphone" function is not working anymore and as such, the white LED light indicator is always off. I have tried uninstalling and reinstalling audio/microphone/keyboard drivers and resetting my BIOS settings already but to no avail. I would greatly appreciate any support or information on how to fix this issue. Thank you for your time.
"Mute Microphone" Function on F4 Key Not Working