How do you unmute combat arms

If you mean unmute as in hearing people talk with MICs again, then while in game, press F8. That will turn voice that back on and you will be able to hear people again. But be aware that not everyone plays with MICs so even if voice chat is on, while in regular games, you may not be playing with people who have or are using MICs.

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But if you are talking about the overal audio output from the game... Try going to your Combat Arms settings and look at the sound FX volume i believe. This should NOT be 0, that may be why you have no sound. If you still have no volume, sometimes it glitches and will mute itself, but only while you stay where you are, so in a room or in a game. But that does not happen often so I doubt that is the cause. If that doesn't work, check to make sure your computer's sound is not on mute or anything like that. If you can't figure it out, try playing some music or something on your computer to make sure it's not your computer or speakers.