This started a few days ago, every time I key the microphone the game completely closes. The microphone is also not found in the system sound settings of my computer.
If the mic doesn't show in the systems settings then the computer thinks there is none -> there is no mic for AH to use.
It may be a drive or hardware fault that causes the mic not to load, and when AH tries to use it there is nothing there and that leads to the crash.
First step would be trying to get it working in Windows. What kind of mic is it (plugged into sound card or USB)?