No Sound

Since 1.7.4 (i guess) I have no Sound in Minecraft. I have re-installed it, installed a new Java version and all, but there's no sound. In the Screenshot you can see that MC is running, but not shown in (any Source of) the Soundmixer. I didn't changed any options in Windows or Minecraft, the volume is at 100%.
I mentioned this problem already to the Twitter Account of the Mojang Support, they had no idea and linked me here.