These steps usually resolve these issues:
1. Ensure the mic works in windows. Do a test recording with the sound recorder. Unmute mic, adjust gain etc, update drivers etc, if it dont work.
2. Start AH in online mode. enter into a txt radio: ".radio 5 yourgameid" - except dont type the quote marks and change yourgameid to your actual game id. And transmit on tunable radio "test 1,2,3". You should hear yourself.
3. If you can hear yourself retune the tunable radio to a range ".radio 5 3" or to another player who is online ".radio 5 anotherplayer" and say something like "radio check" and get someone to reply.
4. If its still not working, go to "Setup", then press the "Voice" button from the clipboard and check the "Use Wave In" option. And repeat steps 2 and 3.
If it still aint working try the technical support forum.