Here is the problem: you have a laptop with built-in speakers as the audio device and microphone as the recording device. And you are pretty sure they have been working fine until lately, they stopped working and are disappeared from the Device Manage, like below:
What to do?
If you know you have mic installed, connected and working, the first thing you should try is this.
Right-click the middle empty area, and select Show Disabled Devices.
And most likely, your audio devices will appear again right in front of you, like this.
The reason it happened is because at one point you had disabled your audio devices and totally forgot to re-enabled it.
If the above tip didn’t do the trick, the next step is to update your sound device driver and you can do so from Device Manager.