A Mac that won't start up is an infuriating problem. If Mac OS X simply doesn't start, then you feel at a complete loss: what can you do to fix the problem? In this feature we take a look at some good advice for what to do when you have a non-starting Mac.

While Apple Macs are well built, and for the most part reliable, they are computers nonetheless and like all computers there are errors that can stop a Mac from booting up correctly. The troubling part about a non-starting Mac is that you can be at a loss how to get started (so to speak). There are many different things that can go wrong and cause a Mac to refuse to start. In this feature we're going to look at 10 steps to follow if your Mac won't start.

Step 1: Check that your Mac turns on

First, let's check that the problem is that your Mac won't start up, and not that it won't turn on - it might sound confusing, but there's actually a big difference.

Press the Power button on your Mac. If you don't hear a start-up chime, and you don't hear any fan or drive noise, or if there is no images, video or visuals of any sort on your display, then your Mac isn't turning on at all.

A Mac that doesn't turn on is slightly different to one that doesn't start up. If your computer doesn't turn on then take a look at this My Computer Won't Turn On support document from Apple. Apple suggests that you:

  1. Check the connection to the power.
  2. Try a different power cord or adaptor (if you have one).
  3. Disconnect all accessories (such as printers and USB hubs).
  4. If you recently installed new memory or a new hard drive, make sure they are correctly installed and compatible (if possible re-install the old memory or hard drive).

If none of these steps resolve the problem, then you should attempt to reset the SMC (see Step 7).

Step 2: The Mac turns on but I don't get a video signal (or it is distorted)

If your Mac does turn on, but doesn't boot up because you can't access the display, then you are most likely having trouble with the display hardware (rather than a broader start-up issue).

If you do see a display, but can't load OS X or log into your Mac, then you should move on to the next step. But if you think it's a problem with your monitor, then take a look at this Apple Support document for advice on troubleshooting a non-working display. Apple advises that you:

  • Check the power supply to the laptop, and power to the display (if using a separate display).
  • Confirm that all cables are connected securely.
  • Check that the monitor is compatible with your Mac.
  • Remove all display extenders, switches and any other devices between the Mac and monitor.
  • Unplug the video cable (if using a separate monitor) and plug it back in.
  • If using more than one monitor in a "daisy chain" unplug all monitors and test using just one.
  • If possible try to use a different display, or a different adaptor (use DVI instead of VGA, for example).

Apple then advises users to try resetting the PRAM or starting up in Safe Mode and adjusting the resolution in System Preferences.

Step 3: Run Disk Utility in Recovery Mode

OS X Recovery Mode

If your Mac turns on, and the display works, but it won't boot, there could be many issues at play. But the one we like to rule out right away - or repair, if possible - is any problem afflicting the hard drive. The easiest first step on that front is to run Disk Utility. On a Mac running OS X 10.8 Mountain Lion or later, you can run Disk Utility by booting into OS X Recovery Mode.

Make sure the Mac is off. (If it's not responsive because it's stuck on a grey, blue or white screen, just hold down the Mac's power button for several seconds until it gives up and shuts off.) Hold down the Command and R keys, and power the Mac back up again.

Eventually, you'll end up on a screen headlined OS X Utilities. (Once you see that screen, you can release the keys you were holding down.) Click on Disk Utility. Then click on your Mac's built-in hard drive in the left column of Disk Utility. (Usually, you'll see two listings for your built-in drive: the first includes the drive's size, like 500GB, in its name; and nested underneath it is your drive's friendlier name. You want that second one.) On the lower right of the Disk Utility window, click Verify Disk, and then wait while Disk Utility does its thing.

See: How do I restore my Mac with Time Machine?

Step 4: Try to Safe Boot the Mac

Safe Boot limits what checks and functionality your Mac focuses on during startup, and performs certain diagnostics. It's rare, but sometimes you can get your unhappy Mac to start up successfully with a Safe Boot, and then restart it normally, and everything returns to hunky-doriness.

Shut the Mac down, and start it up while holding down Shift. Safe Boot can take a while if it does indeed work. To get some feedback about what's happening, you might choose to start up while holding down Shift, Command, and V: that enters both Safe Boot and something called Verbose Mode, which spits out some messages about what Safe Boot is actually trying to do as it goes.

Be patient during your Safe Boot. If the Mac does start up, restart it from the Apple menu once the desktop finishes loading completely. If the Mac starts up normally, go on with your day. Otherwise, keep working through this list.

Step 5: Fsck for fsck's sake

This step is actually kind of fun - at least when it's not your Mac that's under the weather. It's fun because it feels so geeky.

Shut the Mac off, and start it up again while holding Command and S. You're launching Single User Mode. You can release the keys when the intimidating black screen with messages in white text appears.

Wait until the command-line prompt appears, when all the text is done scrolling past. Then you'll type fsck -fy and hit Return. And wait. Possibly for several long minutes.

Eventually, after five different checks that take varying amounts of time, you should get to one of two messages: "The volume [your Mac's name] appears to be OK" or "FILE SYSTEM WAS MODIFIED." If you encounter the first message, type reboot and press Return. If you see the latter message, though, you'll want to run fsck -fy all over again. You can retype the command and hit Return, or press the Up arrow once and then press Return.

Ideally, you’d eventually get to the "…appears to be OK" message, type reboot, and find that your Mac now starts up perfectly.

If this doesn't work, and your Mac still doesn't start up, then move on to the next step.

Step 6: Reset the NVRAM, because why not?

In the PowerPC days, we talked about resetting the PRAM. On modern Macs, the real term is resetting the NVRAM. The name refers to special memory sections on your Mac that store data that persists even when the Mac is shut off, like volume settings, screen resolution, and similar options.

Resetting that data isn't harmful, but quite frankly it's also rarely genuinely useful. But man, at this point, it can't hurt.

You might need to grow an extra finger or two for this one, or have a friend help you out. Hold down all of these keys: Command, Option, P and R, and turn on the Mac. Keeping holding the keys down until you hear the Mac restart again. Apple says to let it restart just the one time; I usually listen for a second reboot, and then release the keys.

In some cases, after performing this step, your Mac will restart normally. In other cases, you might instead see a progress bar on startup. If the progress bar fills up and then the Mac starts up, you're probably good to go. In some cases we've seen, however, the Mac shuts down at around the halfway point in the progress bar.

Step 7: Reset the SMC

In some situations, you may need to reset your computer's System Management Controller (SMC). This is largely a last-ditch attempt to fix the current version of Mac OS X before attempting to recover the data and moving on to re-installing OS X. Apple has a detailed article online that guides you through the SMC reset process.

See: Resetting the System Management Controller

Step 8: Target disk mode

This step should be taken prior to Step 9 and it depends on your backup situation. You do make regular backups, right? If you're not sweating at the moment, confident in your Time Machine or other backup solution then go ahead to Step 9. But if you wish you'd backed up your Mac then now is the time to see what you can salvage from the machine.

For this, you'll need a second Mac. If you haven't got one then ask a friend. Follow these steps to use Target Disk Mode:

  1. Connect both Macs together using an Apple Thunderbolt cable (it also works with FireWire cables on older Macs).
  2. Swift off your Mac (hold down the power button if necessary).
  3. Start up your Mac while holding down the T button on the keyboard.
  4. Keep holding the T button down as you hear the startup chime and keep it pressed until the Thunderbolt icon appears on your screen.

This places your Mac in Target disk mode. In Target Disk mode your Mac acts like an external drive. You should now, hopefully, see the hard drive for your Mac on your second Mac's Finder. You can grab the files you need from your hard drive, or even clone the entire hard drive to another external drive.

How to back up your Mac: Three types of backup all Mac users should be using

Step 9: Reinstall Mac OS X

Remember OS X Recovery from Step 3? You can use it to reinstall Mac OS X too. Boot into Recovery mode, and then click to install Mavericks and follow the on-screen prompts. See Use Recovery mode to restore your Apple Mac computer.

This article - How to reset a Mac: restore your Mac to the original factory settings - has more information on cloning hard drives and reinstalling Mac OS X.

Step 10: Make a Genius Bar appointment

If you've made it this far and your Mac doesn't work then you will need to take it in to an Apple Genius Bar to see if they can help you fix it (or arrange for a repair under warranty). Hopefully you have got enough data from your Mac so as to be able to back up, or continue working on a new Mac.

See: How to book an appointment with Apple's Genius Bar