I don't have sound when I start up and play Minecraft

When I start up Minecraft I don't have any sound. First I thought that my sound was turned off, but it wasn't. So I restarted the game and I stil had no sound. A few days later I went to play Minecraft and the sound was back again, but when I later that day wanted to play Minecraft the sound was gone. I think that there meaby is something wrong with the soundengine. I play with the new launcher and my system is Windows 8.1. I hope that you guys can do something about it because it is really frustrating when I have to restart my game like 4 times and still have no sound at all.
Allready Thanks,
Derk aka DerkGuitarNL