Ahhhhhh........ I may have an idea about this, I had similar, I also had realplayer and windows media player installed amongst other viewers.... go into those and turn the volumes up, on mine even though the windows volume was set at its highest, for some stupid reason in some programs like games, the realplayer volume control which was turned right down was the overiding factor and was preventing my PC volume from working as it should.
does that make sense?