No audio received whilst on the internet

Hello,
Yesterday i was tryn to play a video file online and it started to play,but there was no sound. I thought the audio was missing. Then i tried playin sum musik files on my computer (which worked)> lastly i tried playin several musik videos on youtube that im sure has audio and they were playin but there was no sound. I restarted the comp and stil the same problem today. Can anyone help me? It would be greatly appreciated.