Antwoord op "What causes the loss of sound problem on the MacBook Air?"I had that problem after a forced shutdown while the system was delaying to boot in restore mode (Command +R). After that, I had no internal speakers, built-in nor startup chime. After some days trying every step I found in the Internet I was decided to change the sound board. The computer was left all the night doing backup and in the morning without realizing it was sleeping I forced shutdown accidentally by pressing the on button too long. Surprisingly after reboot the chime came up again. So there is my doubt. A forced shutdown may cause a system fail to no recognize the internal audio board?