What happens if you shut it down & restart just holding onto the option key? That should give you the “Startup Manager” screen which will let you choose a startup disk; more details from Apple’s site. Also if you have a USB drive—thumb drive or other kind of drive—you might be able to boot from that to get some kind of disk repair to happen.
When you boot up from another disk, I would recommend Disk Utility repair the disk. If that does not work—and you are sure there is nothing on the disk you need—then perhaps you can erase the disk. But that is a bit of a radical solution.
I would recommend launching Terminal form the USB disk and then looking at your disk usage. Maybe the disk is full or near full? If so, that might be the problem. I would then recommend you go find something you know is taking up space and simply delete from the command line.
The first command I would recommend you run is ls -lah
on the /Applications
directory like this:
ls -lah /Applications/
Look for any large sized files you can toss. The most obvious one in my mind would be the Mac OS X 10.10 Yosemite installer. It should be named Install OS X Yosemite.app
. To get rid of that just run this command:
rm /Applications/Install\ OS\ X\ Yosemite.app
The backslashes are to escape the spaces. You can also run it like this with quotes around the filepath:
rm "/Applications/Install OS X Yosemite.app"
After doing that, try to reboot from your MacBook Air’s hard drive. It should work.
When you are back in the system, I would see about clearing out more space. First, manually look around for stuff you are 100% positive you can toss or copy elsewhere like stuff in your personal ~/Documents/
directory. Then I would recommend you download Onyx
. There are different versions for different OS versions and while it doesn’t seem like a Yosemite version has been released yet, I would expect that to appear in a few days. Run that to clear out deeper system data & caches that might be taking up space.
UPDATE: According to the comments from the original poster, the system disk for the MacBook Air won’t even mount. If that is the case, then I recommend resetting the PRAM or NVRAM depending on the make/model of your MacBook Pro.
Instructions for dealing with the PRAM are here on Apple’s site; ignore the title that refers to Mavericks since those instructions should work with all version of Mac OS X:
- Shutdown your Mac.
- Start your Mac.
- Immediately hold down the command + option + p + r keys.
- You will hear the Mac OS star up chime once, and then once more as it restarts form the PRAM being reset. After the second “BONG” sound let go of the keys & boot up as normal.
Instructions on how to reset the NVRAM are here. It seems a tad more daunting but not really that hard to do:
- Shutdown your Mac.
- Start your Mac.
- During starup hold down the command + option + o + f keys.
- When you get into open firmware—which should look like a terminal prompt—type in the following two commands:
reset-nvram return
reset-all return
Your MacBook Air will now restart with cleared NVRAM settings.
option
key? That should give you the “Startup Manager” screen which will let you choose a startup disk. Also if you have a USB drive—thumnbdrive or other—you might be able to boot from that to get some kind of disk repair to happen. support.apple.com/kb/ht1310 – Giacomo1968 Oct 19 '14 at 16:34