Provided the system's hardware is working properly, then you may see a blinking question mark if a boot volume cannot be found, but beyond this you may see a prohibitory sign show up on the screen. Generally when the prohibitory sign shows up, you will initially see the gray Apple logo, followed by the presentation of the prohibitory sign after a few moments. This indicates that the system has found and recognizes your installed OS as a valid OS, but cannot boot from it because of some problem with the system. If this occurs, then there are two things you can do to fix it.
Boot to Safe Mode Usually this problem happens because some kernel extension cannot be loaded or configured properly during bootup. If you have manually tampered with your system's extensions and have inadvertently edited one or changed permissions on it, then the system may not load it properly during start-up. If the extension is a nonessential extension, then booting into Safe Mode may allow you to fully boot the system, from which you can then try running permissions repair routines.
To do this, power down your system and then start it up with the Shift key held down, and if the system loads then open Disk Utility, select your boot volume, and then run a Permissions Fix routine on it. After the routine completes, restart the system and hope you can boot without the prohibitory sign. Anyone know what to do now? Fabulous - just before going to see a movie this happened, but thanks to this post, I solved the problem in 5 minutes.
OSX Yosemite cannot boot when TRIM is enabled on third-party SSD
I did it wrong the first time, THEN read more carefully! Worked like a charm! This problem would have made me crazy!!!! I don't have a red light showing through the headphone jack, and I've never used the headphone jack before today, trying to fix the problem. I can't even hear music through the jack. Thank you so much! I didn't stop the sound the first time and it didn't work. Make sure you pause the song I did it in iTunes , made sure it was on "Output" on the sound tab and it reset. Thank you thank you thank you!
Thanks a ton bro, you gotta pause the music or it won't work. Took a couple tries but deff made my night. Why does Apple or who ever not bring a update for this problem since apperently so many people are suffering the same issue This was a lifesaver! Sound was not even coming through the earphones. I shut down my MacBook Pro first, restarted and it solved that problem. Then proceeded per the instructions. This problem happened after I used a set of powered speakers with the computer for the first time.
I tried fixing the problem as above plugging the power speaker jack back in. Then I tried again plugging in my iPhone's headphone jack instead. Then it worked! I guess some jacks are more compatible with the MacBook than others.
Macbook "No entry" sign at startu… - Apple Community
It's strange whatever is going on on the inside. Didn't work for me. It switched to digital output. But still has red jack and muted sound. The above didn't work for me, nor restarting. The red light went out and "Internal Speakers" appeared in the list where it should be. Try it with or without the headphones plugged in, whichever works. Another thank you to go on the list. So grateful; like others I had to try it twice, but very relieved.
Prohibitory symbol
Good to read alternative options in comments too. Best wishes from Lisbon, Portugal. Joe here, blog owner. For what it's worth, the procedure I've outlined above doesn't always work for some reason. If you've read this far, I'd suggest trying IT2's solution from a few lines up. I was going bonkers but it worked. Sending a happy hug. Can you handle another expression of gratitude?
Have had the problem in the past, didn't remember what I'd done to remedy, tried this and it didn't work and second time it did. Thanks much for sharing! Woo Hoo! Took a few times. Like others, I missed the part about turning off the sound. Finally worked with IT2's solution. With headphones in, hit mute on and off, pulled out the headphones and I have speakers again!
Just had this exact thing happen.
Did a quick google search and came across your site. The fix worked exactly as you described Joe. This didn't work for me. I unplugged the headphones and it set itself back to optical. IT2's solution did not work either. I just fixed the problem, after none of the above worked, by just plugging in and unplugging the headphones like 15 times. If I pull out headphones, yes, it changes to digital out, but then the icon greys out again and I am once again unable to alter the sound levels.
However, I am please that I can at least use headphones or speakers cuz I am currently deep in a rustic cabin deep in the rainforest and my laptop is my sole amusement once the sun goes down. I will try someone else's suggestion of plugging and unplugging the external speakers fifteen times next as that was what was last plugged in. Thanks so much for putting this up. I would have never been able to work that out! Thanks again. None of these worked for me, but eventually I jammed a plastic tube the inside of a pen into the socket and rotated counterclockwise.
After a few tries it worked! Definitely a stuck switch. Saddly, It didn't work! Help me! This has been annoying me for a few days now and with your advice, YOU fixed it for me in less than a minute! However the Toothpick trick DID work!!
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I thank you so much for this link! Thank you so much. Your help was unbelievably perfect. Now I can play my music. Thank you for your excellent help!!!! I am so happy! Fiddled with it for ages! I have a 8GB USB stick, i formatted it in disk utility with a GUID partition for it to boot and then selected the Snow leopard image, dragged it to source and then dragged the usb to destination, doesn't go past that error.
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