So weird, I was just having this same problem, same day too.
I was able to fix it by going in to System Preferences > Sound, while playing music through the internal speakers (having nothing plugged into the headphone jack).
From there all I noticed was the Internal Speakers option, like you. Once I plugged in a set of external speakers into the headphone jack, the Headphones option popped up where the Internal Speakers option was, and the Mute box at the bottom was checked. Un-checking it fixed the whole problem. I'm not sure how that would get enabled in the first place. Obviously music played fine through the internal speakers, and the computer itself was NOT muted, just the Headphones were.
Weird, but it worked. If that doesn't fix the problem, try a restart. If nothing else, time to visit the Apple Store. Good luck.
Thanks...followed your advice but the headphones option does not show up when i plugged in a set of external speakers - even when i was playing music through the internal built in speakers. I think it must be an hardware problem: the jack port must be broken or something, as nothing happens at all when i insert different jacks (speakers, headphones etc). I wonder whether you or anyone knows whether this is a relatively simple repair, or i need to change the whole sound or logic board. thanks.
Hey! so this EXACT problem started yesterday as well. This is particularly annoying because I previously had this problem in August '11 and after 3 visits to the Apple store, 1 complete re-formatting, 1 replacement of logic board, Apple staff finally gave up on trying to find a solution and [thankfully] gave me a 2nd machine. ...and now this one is having the same problem. .... :'(
What the mac?!
Are you using active speakers or passive speakers. Active speakers , ones with their own power supply, are meant to be plugged into the line out, instead of headphone jack. Typical headphones(passive) are in the 75-600 ohm range,so Mac will detect when they are plugged into the headphone jack . Active speakers on the other hand present more than 10,000 ohms to the headphone jack, so they are not detected(as far as Mac is concerned, they are not even plugged in).
This is not true, atleast in my experience.
I've used 2 sets of active (powered) speakers with my MBP, and have always used the headphone jack. In fact, I tried several times (both on purpose, and accidently) to connect them through the 'line out' jack to no avail. When I disconnect the speakers, or even headphones, any audio that was playing continues to play through the internal MBP speakers. I don't know if this is something just with older Macs (mine is a 2007 model, running 10.5.8), or it's just something I've somehow changed in the settings.
I'm not sure the exact ohms level of my speakers, but they're a decent set of Logitech, 5 channel speakers with a subwoofer.
All recent MacBook Pros have 2 jacks.
1) Combined lineOut/Headphone/SPDIF(optical). So if you plugin a headphone,it willshow up. If it does not, an the plug is of correcttype, either line out , or digital out will be enabled.
2) Combined Mic/LineIn/SPDIF.
Mac Pros on the other hand have dedicated headphone output, and it will work if a headphone is detected.
So in short , on a MBP,headphone jack , and line out jack are the same jack.
This worked for me:
Go to System Preferences
Click "Sound" icon
Go to bottom of window and make sure "Use audio port for:" is set to "Sound Output" and not "Sound Input"
Evidently, when I plugged in a USB microphone, this reset to "Sound Input", so I needed to reset it to "Sound Output".
Hope this works for you.
I have this same problem.
I noticed that this only happens when I used an audio imput jack with 2 insulators (the little black lines on the metal part that goes into the computer), but whe I used an imput jack with 3 insulators (the ipod earphones that have a microphone on them have 3) it would play through the earphones. but my Dre Beats, which have only 2 insulators wouln't even be recognized by my MacBook Pro.
Could this maybe have something to do with this problem?