Audio is deactivated after each reboot on Yosemite After clean installing Yosemite and rebooting my MacBook Pro, audio seems to be deactivated, although the sound is active and I can use it. But I can't change the volume. The icon in the menu bar is grayed out:



If I run

sudo killall coreaudiod


in the terminal, it is activated and I can use it as usual again.

What could cause the problem and how can I fix it?
Have you tried a NVRAM and SMC reset?