No Audio when online

OK here is the problem, I hear no sound when online, there are sound when I play music, and when my system load my mother board speak as it always has, but when I try to listen to almost anything while on line there is almost nothing. my control say I have no audio device and no mixer, can anyone help me correct this problem?
Yesterday my wife told me when my grandchild was playing a PBS games on some there was sound and on other there were none, so we know there is no problem with the sound card