Imac Starts To Boot Then Shuts Down

1) Restart while holding down the Option key immediately after pressing the power button (Don't let go until it starts from the disk or locks up). This should bring up the Startup Manager and would allow you to select the startup volume. It may work if the computer is stuck, and can't find the correct startup volume! I reformatted the hard drive of our iMac using the disk utility and re-installed the OS. It worked for a day and now every time we turn it on we get a chime, the Apple logo shows up about half way through the boot up it shuts down (never booting up). The steps are listed in order, so start with the first one, see if that helps, and then continue with the next one if it doesn't. 1 Check the Mac's Power Connection Make sure the Mac is powered up properly by checking the electrical connections.

Your Mac displays an Apple logo when it finds your local startup disk, which is a startup disk built into your Mac or directly connected to your Mac. As the startup process continues, you should see a progress bar with or without the Apple logo. This screen may alternate with a blank screen several times.

If you're installing macOS, the Apple logo or progress bar may remain on the screen for much longer than usual after your Mac has restarted. As the installation continues, the progress bar may move slowly and pause for long periods. That's why Apple recommends starting macOS installation in the evening – so that it can be completed overnight, if needed.

If you feel like you've waited long enough to know that your Mac has got stuck on this screen, follow these steps.

The following steps are only applicable for Mac computers with an Intel processor. If your Mac with Apple silicon is stuck on this screen, please contact Apple Support.

Boot

Mac Starts To Boot Up Then Shuts Down

  1. Press and hold the power button for up to 10 seconds until your Mac has turned off.
  2. Try using safe mode to identify the issue.
  3. If the issue persists, unplug all accessories from your Mac, including printers, drives, USB hubs and other non-essential devices. (There may be an issue with one or more of these devices or their cables.) Once more, press and hold the power button for 10 seconds, then press it again to turn your Mac back on.
  4. If the issue persists, turn off your Mac again, then turn it back on and immediately press and hold Command (⌘) and R to start up from macOS Recovery.
  5. While in macOS Recovery, use Disk Utility to repair your startup disk.
    • If Disk Utility didn't find any errors, reinstall macOS.
    • If Disk Utility found errors and repaired them, restart your Mac. If the issue persists after restarting your Mac, reinstall macOS.
  6. If you still need help, please contact Apple Support.

These key combinations apply only to Mac computers with an Intel processor, not Mac computers with Apple silicon.

Mac Shuts Down On Boot

To use any of these key combinations, press and hold the keys immediately after pressing the power button to turn on your Mac, or after your Mac begins to restart. Keep holding until the described behavior occurs.

  • Command (⌘)-R: Start up from the built-in macOS Recovery system. Or use Option-Command-R or Shift-Option-Command-R to start up from macOS Recovery over the Internet. macOS Recovery installs different versions of macOS, depending on the key combination you use while starting up. If your Mac is using a firmware password, you're prompted to enter the password.
  • Option (⌥) or Alt: Start up to Startup Manager, which allows you to choose other available startup disks or volumes. If your Mac is using a firmware password, you're prompted to enter the password.
  • Option-Command-P-R:Reset NVRAM or PRAM. If your Mac is using a firmware password, it ignores this key combination or starts up from macOS Recovery.
  • Shift (⇧): Start up in safe mode. Disabled when using a firmware password.
  • D: Start up to the Apple Diagnostics utility. Or use Option-Dto start up to this utility over the Internet. Disabled when using a firmware password.
  • N: Start up from a NetBoot server, if your Mac supports network startup volumes. To use the default boot image on the server, hold down Option-N instead. Disabled when using a firmware password.
  • Command-S: Start up in single-user mode. Disabled in macOS Mojave or later, or when using a firmware password.
  • T: Start up in target disk mode. Disabled when using a firmware password.
  • Command-V: Start up in verbose mode. Disabled when using a firmware password.
  • Eject (⏏) or F12 or mouse button or trackpad button: Eject removable media, such as an optical disc. Disabled when using a firmware password.

If a key combination doesn't work

If a key combination doesn't work at startup, one of these solutions might help:

  • Press and hold all keys in the combination together, not one at a time.
  • Shut down your Mac. Then press the power button to turn on your Mac. Then press and hold the keys as your Mac starts up.
  • Wait a few seconds before pressing the keys, to give your Mac more time to recognize the keyboard as it starts up. Some keyboards have a light that flashes briefly at startup, indicating that the keyboard is recognized and ready for use.
  • If you're using a wireless keyboard, plug it into your Mac, if possible. Or use your built-in keyboard or a wired keyboard. If you're using a keyboard made for a PC, such as a keyboard with a Windows logo, try a keyboard made for Mac.
  • If you're using Boot Camp to start up from Microsoft Windows, set Startup Disk preferences to start up from macOS instead. Then shut down or restart and try again.

Remember that some key combinations are disabled when your Mac is using a firmware password.

Learn more

  • Keyboard shortcuts that you can use after your Mac has started up.