Macbook Pro's internal speaker is not recognized
Hello, I've been using my macbook pro 15-inch(early 2011) for almost a year.
I usually connects external speakers to my macbook pro. However today my mac started not to recognize any speaker devices. As I disconnect my external speakers, my mac doesn't even recognize its internal speakers. When I go to my system preferences, it usually display the message 'No digital output available' or says that it recognizes external headphone EVEN when it's not connected to the macbook pro. I always try putting my sound volume to the maximum but still no sounds come from the internal speakers. The mac constantly stop recognizing the internal headphone and switch to the external headphone automatically when nothing's connected to the mac. I have been searching through internet and rebooted my mac more than 3 times but this still happens. I am not even sure if this is software or hardware's problem. Can anyone identify what would be the cause of this problem?
I would appreciate if anyone answers my question.
MacBook Pro, Mac OS X (10.7.3), Macbook pro 15inch