iMac Pro iMac volume greyed out

[key2]

Hi,

My 2011 27" iMac will not play sound through the internal speakers, in fact I can't select internal speakers as this option has completely disappeared. I am running 10.13.4.

I have restarted the mac and even created a new user, reinstalled the OS and unplugged everything from the mac but nothing helps.

Any suggestions would be much appreciated.

Thanks
Paul

 

[DeltaMac]

Have you tried an NVRAM reset?
Restart, holding Option-Command-P and R
You should hear your boot chime sound.
Keep holding the same 4 keys until you hear the boot chime two more times, then release the keys to let your iMac boot normally.
Once booted up, go to System Preferences, then Startup Disk, and select your boot drive. The NVRAM reset clears that setting.