FSX ATC/Other Voices are Mute?

I've had FSX ( microsoft flight simulator X) for about three years now. Everything has worked great up to recently when I got a new computer and had to reinstall the game. All my saved flights and completed missions loaded onto the new computer and everything was exactly the same except for the fact that you can't hear ATC or the Copilots (copilots in missions only). I went sound settings and turned up "voice" but it didn't make a difference. Pretty much what happens is I'll be flying along with a lot of engine/background noise and suddenly all of the background noise will dim down really low and I know that either ATC is talking to me or my copilot is but I can't hear there voice. Once their done talking the background noise comes back up and I have to go look at the kneeboard or ATC window to figure out what they said. It's really a pain and no fun at all.

Any suggestions as to how to fix this problem??

Thanks!