I had to reinstall OS X Lion Server 10.7 on my Mac mini (late 2011) due to partition and boot record corruption. Since reinstalling, I have not have sound. The only sound device that shows under Utilities > Sound is "Internal Speaker". Previously, "Headphones" also appeared. I have a Harman Kardon Soundsticks 2.1 sound system. It has only one sound connector. I always plugged it into the green port on the mini. It worked fine. Since reinstalling I have no sound at all. Any ideas out there? Solutions? I've been through the Cmd-P-R deal, reinstalled OS X Lion Server - all to no avail.
~/Library/Preferences and trash your
com.apple.systemsound.plist file. Drag it right into the trash. Empty trash and restart your Mac.
A new plist file will generate automatically, look for the speaker/sound icon in your Finder menu. If that doesn't resolve the issue, try Command ⌘-Option ⌥-P-R again during reboot and make sure you hear the Apple chime at least two times for a full recycle.