In case you experience sound problems in Arma 1 or no sound at all, please try this:
1. Create a system restore point, just in case:
http://windows.microsoft.com/en-US/windows7/Create-a-restore-point
2. Open Windows Control Panel, go to Hardware and Sound --> Sound.
3. Delete all sound playback devices except the default one (usually the speakers).
4. Try running the game again.