Then reboot your PC and you will be enabled to voice chat or send message in games using Discord Overlay.
In addition, corrupted or missing game files might also cause mic not working in CS:GO.
That said, you should still check the in-game settings, just in case.
Depending on the cause of your microphone issue, the solution is going to be different, which is why we will guide you through all of the potential solutions using the knowledge that the CS: GO community has collected over the years.
Voice Chat Pushing down the k key will allow you to communicate with a microphone.
Using the in-game voice chat may not always be possible, however.