You pressed the Power button to start your Mac up. After a little while, instead of showing the normal login window, something else appears instead. Do you recognise it, understand what it means, and know what to do next? Here’s a short guide.

🚫 (in grey) – the Prohibited symbol

There’s something wrong with the startup system on your startup disk. Shut your Mac down by pressing and holding the Power button, then try again. If you don’t have another startup disk you can use, try again with Command-R held to enter Recovery mode, use Disk Utility there to check and repair your startup disk, and see if that solves the problem. If not, you’ll need to re-install macOS, again in Recovery mode.

? a question mark on a Folder icon

This has essentially the same meaning as the Prohibited symbol above, and the same solutions.

A grey, blank screen

This can indicate a problem with starting up from your startup disk (see the Prohibited symbol above), or could represent a hardware fault. Try starting up in Recovery mode; if that doesn’t work, hold the D key during startup instead and see if you can enter Diagnostics.

A completely black, dead screen, with no sign of life

This is most probably a hardware failure. Check that mains/AC power is getting to the Mac. If it is and there’s still no sign of life, this is likely to require a service technician.

 (white Apple logo) and/or white progress bar

This is, of course, perfectly normal before displaying the login window. If it’s much slower, or appears to be stuck, it may indicate that an earlier installation or update is still completing, or sometimes that repairs are being made to the startup disk. If you can, give it up to an hour to see if it’s going to progress. If it appears to be stuck, you can try forcing a shutdown by holding the Power button, and starting up again. If it still just gets stuck, start up in Recovery mode, check and repair the startup disk and re-install macOS.

If you have peripherals connected to your Mac, consider disconnecting them, leaving just your mouse/trackpad, keyboard, display, and network connection. It’s always helpful to keep your mouse/trackpad and keyboard connected to USB ports instead of relying on Bluetooth when your Mac is having problems starting up, so that it responds reliably to keyboard controls in particular.

⚠️ (warning triangle in grey) on a grey globe

This means that your Mac has been unable to start up in Remote Recovery mode, and may be because it hasn’t been able to establish the required Internet connection. Check that your router is fully connected, and if possible connect an Ethernet cable between your Mac and that router, to avoid having to use Wi-Fi. If you’re certain that its Internet connection is sound, and nothing is blocking its access, then the only way ahead is to try starting up in normal Recovery mode, or from a bootable external disk.

🔒 a padlock in grey

The firmware password is required to continue starting up.

Prompt for a 4 or 6 digit PIN code

This Mac has been locked remotely by Find My Mac. Enter the PIN code to unlock it.

Thunderbolt, USB or FireWire symbol

This Mac is in Thunderbolt, USB or FireWire Targest disk mode. Start the connected Mac up to access it.

A message that it restarted because of a problem

If you’re invited to click on a button to see the report and send that to Apple, do so. This is almost certainly going to be a Panic Log, which I’ve detailed here.

Your Mac restarts repeatedly

If your Mac never gets as far as the login window, this is most probably a kernel panic during startup causing a boot loop. Shut it down and read this article.

If this occurs later, it may be fixed by starting up in Safe mode, with the Shift key held, where you can work out what needs to be removed, updated or fixed.

Your Mac starts up in Windows

Welcome to Boot Camp!

Apple’s guide is here.