Macbook Pro's internal speaker is not recognized

Question

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.

Answer 1

Look into the headphone port. Can you see a red glow? If so, an out-of-spec analog headphone plug jammed the digital port's contacts in the "mute speakers" position.
The official fix is a new logic board but that;s overkill. Most people are able to free the contact by inserting a plug about 3/4ths of the way in the port ahd GENTLY moving the plug in the horizontal plane.
To prevent recurrences, stop inserting the external speaker plug "to the hilt." The tip-to-shoulder distance on the plug is too long for the precision port. Turn on an audo source, fire up the speakers and then start inserting the plug; when you hear sound in both channels, stop pushing.
In the image below. I have a pair of name-brand headphones attached to my MacBook Pro. Note the shoulder of the plug is NOT touching the computer case. This position gives normal sound and the plug is as secure in the jack as if I'd shoved it all the way in. And nothing is jammed.