so i was playing single player last night, and i played for about 3+ hours without any sound during fighting. The music played, and the build sounds were working, but i didn't hear any voices, warnings, or explosions\weapons firing. I kept thinking that there were sounds for these cause i had heard them before. I hit escape, went to sound, hit restore, save, and then exited that menu and went back into game. And the sounds came on.

So basically, i had never gone into sound options before, and they had worked before this round.