No audio in imac after upgrading to OS X Lion

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I recently upgraded to Lion on my Imac. The whole thing worked fine, including the audio. Then I installed ProTools .After the ProTools installation, Audio stopped working. ITunes does not play. Garage Band won't even load. I'd simply Google the essential audio driver, download it, and move on. However I am unable to locate such driver when I Google it for a mac.Can someone please help?

[Phalguni88]

I recently upgraded to Lion on my Imac. The whole thing worked fine, including the audio. Then I installed ProTools .After the ProTools installation, Audio stopped working. ITunes does not play. Garage Band won't even load. I'd simply Google the essential audio driver, download it, and move on. However I am unable to locate such driver when I Google it for a mac.Can someone please help?

Trying looking in "Audio-Midi-Setup.app" in Utilities folder within the Applications folder, if the audio devices are listed there.

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Tried that, however when I click on the Audio-Midi icon, nothing happens. The icon heading turns from blue to gray, although that's it. No application opens up. No folder, nothing happen. It's like the whole audio system has been zapped.