Q: Just installed lion...no sound

had the same issues with no sound first being output to the miniDP, to HDMI tv.  Now no sound from internal speakers on my MBP 2011 very annoying.  I thought apple was meant to be good but I'm starting to wonder why I left windows, ipods, iphone, itunes and now my new MBP all have some major faults.  Put it this way I never lost sound on my 4 year old xp desktop.

Anyway that said...I plugged in some headphones had sound on them then unplugged them and it was back, RIDICULOUS.  But it worked.

I experienced the same issue and after trying several things I finally repaired permissions which instantly fixed the problem.

Maybe try Onyx as well, great tool!

http://www.titanium.free.fr/download.php?sid=944df94a3f150781b84384b8f2a8da52

Darn.  Nothing.  Attempted step-by-step and no luck.  Thanks anyways.

Just installed my SSD today in my UniBody MacBook Pro 15" and my sound was gone... After reading a couple threads I then went to Finder->Go->Utilities->Audio MIDI Setup.app and on the left right clicked on "Built-in Output" and selected "Use this device for sound output" and WOALA!! :-) Hope this helps!

I had same issue and noticed my headphone jack had a red light turning on and off. I did more reading and found that the switch in the headphone jack was stuck. https://discussions.apple.com/thread/3694502?start=0&tstart=0 This may not apply to this thread but it helped me.

Wow, I just read a TON of posts and don't see solution ... installed OSX Lion, then a week later my JBL Creature speakers STOPPED WORKING. Any help is appreciated!

Variant on the problem with my mid-2011 MBA - sound had worked fine for 9 months, then suddenly nothing: neither speaker nor headphones working. Was prepared to repair permissions, but a simple reboot fixed it. Go figure.

After upgrade, I had this problem. Restarting didnt solve the problem. So I turned off my macbook and removed all the plugs and headset then turned it on again. Now it is running smooth again. I hope this helps.

Still have no sound from external speakers. Have tried numerous options, including the following that I picked up from many others with the same problem (no sound from headphones/external speakers after installing Lion OSX. May have started after I used Facetime for the first time after Lion was installed.)

I.  1. Delete the User and System Cache folders. Reboot and then empty trash. Before you reboot, perform step 2 at the same time.

2. When restarting the computer, reset the PRAM.

II.  ~/Library/Preferences.  Click Go. Move the   com.apple.soundpref.plist    file from the Preferences folder to the Trash. Restart.

III. Permission repair. Press down "command, R" and start. A menu appears. Select a language (preferably one you understand). Another menu with 4 options appears. Choose the last one: utility disk (it's the same as the one you can access in the utility folder in Lion). Select your mac hard drive (Macintosh HD) and go to S.O.S. First check permissions (I had a warning about one file, but it seems it's normal), and then repair permissions.

Still looking for help w/this issue. Thanks! :-)

I had the same issue.  When I went to System Preferences and Sounds I realized the system had switched to LogMeInSoundDriver for the sound output.  This must have happened when I logged in earlier today with logmein.  Normally, once the connection is stopped the computer went back to normal but apparently this is no longer the case with Mountain Lion.

Solved! - at least for my computer. Here's the story...I tried, tried, and tried to fix this based on everyone's thoughtful suggestions - short of rebooting in safe mode.  Then, just before picking up the phone to call in paid help, I tried the simplest of the simple.  In iTunes, at the top of the menu bar just to the right of the volume slider bar is the Airplay icon - the little rectangle with an intersecting triangle.  See it?  I clicked on it and the dropdown menu gave me a choice of "Computer" or "Apple TV."  Apple TV was selected.  I clicked on "Computer" and out blasted iTunes music!  Hope it works for you.

Manually deleted old files like ones below from

Library > Preferences > Audio  (these were outdated - spread the word!)

Library > QuickTIme

CanonMJPEGAVI.component

CanonMJPEGAVIDec.component

CanonText.component

DesktopVideoOut.component

DVCPROHDMuxer.component

DVCPROHDVideoDigitizer.component

DVCPROHDVideoOutput.component

DVCPROHDVideoOutputClock.component

DVCPROHDVideoOutputCodec.component

FCP Uncompressed 422.component

Google Camera Adapter 0.component

Google Camera Adapter 1.component

LiveType.component

macam.component

AmpliTube2DUOLERW.vst

StudioDevilBVC.vst

DVCPROHDAudio.plugin

Sound works on 15" MBP from 2010 !!!!