During my time with Apple, this was something I heard about umpteen times a day. What it usually means is either a failed hard drive, hard drive cable, or, directory damage that is stopping the unit from booting. Rarely, it’s a problem with the operating system, but, usually it’s one of the first 3. Read more below the fold!
An easy way to check this out is to force reboot the computer and hold down these 2 keys: COMMAND and the S keys simultaneously, which puts the computer into a mode called “Single User Mode.” This mode will cause the screen to turn black and display a whole bunch of white text, similar to an old DOS computer. When you see this text, you can let go of the keys. At the end of this stream of text, you will eventually get a prompt where you can type on the keyboard. Type this line of text just as you see it, with the spaces between:
fsck -y -f
Hit return on the keyboard and wait. Eventually, it’s going to either pass or fail–if it fails, you will see something that states the Macintosh HD could not be repaired, or maybe disk I/O error in that text. If it fails with either of these faults, you will most likely have to either erase the hard drive, or, replace the hard drive and cable. What you are seeing is directory damage, which can happen to anyone at anytime for any reason and it will prevent the computer from booting. Sometimes, the directory damage will be small and the built-in utility can repair it enough to get you on your way. Otherwise, you would need a higher strength disk utility such as DiskWarrior.
If you are nervous about doing any of this on your own, it’s Capital Mac to the rescue! Contact us for any types of gray screen or stuck at the Apple logo that you may experience on your Macintosh. We’re here to help!