Are you playing in windowed mode? If so are you using a controller?
If yes to both, click on the game screen with your mouse. I've had the issue a few times where I was controlling in game but had been browsing between loading and playing and the sound was gone. If no to both I can't help other than suggest driver updates.
FFXI:Sylph - Perrin 75 Hume THF; Retired (At least from my use any way)
EVE Online:ScraperX; Retired
WAR:IronClaw- Peryn SW;SkullThrone- Grymloc BO; Retired