iMac Won't Turn On or Boot: What to Check First

If your iMac will not turn on, check the power cable and wall outlet first, then reset the SMC: unplug the iMac for 15 seconds, plug it back in, wait five seconds and press the power button. If there is still no sign of life, the power supply or the logic board is the likely cause, and both can be repaired. If it powers on but will not finish starting up, showing a flashing question mark folder or stalling on the Apple logo, the drive or macOS is more likely, and your files are often still recoverable.

First, pin down what "won't turn on" means

Very different faults get described the same way. Press the power button once, then watch and listen for a minute:

• Fan: put your ear near the back of the iMac. A fan starting means the power supply is delivering at least some power.
• Drive: on models with a hard drive you may hear it spin up. Clicking, grinding or a repeated whirr-and-stop is a warning sign for your data.
• Chime: older iMacs chime every time they start. On 2017 and later models the chime depends on the macOS version and a setting, so silence on those is not a fault in itself.
• Screen: note whether it is black, black with a faint image, or shows the Apple logo, a progress bar or a folder with a flashing question mark.
• Keyboard: on a wired keyboard, press Caps Lock. If its light comes on and off, the iMac is running even though the screen is black.

Step-by-step checks

Work through these in order. None of them needs the iMac opened, but if the drive is clicking or grinding, skip straight to getting your data off (below).

1. Power cable and outlet. Plug a lamp into the same outlet to prove it works. Plug the iMac straight into the wall rather than a power board or double adaptor, and push the cable firmly into the back of the iMac, where it can work loose after a move. Try another suitable cable if you have one.
2. Reset the SMC. The System Management Controller looks after power, fans and sleep. On an Intel iMac, shut it down if it is on, unplug the power cable, wait 15 seconds, plug it back in, wait five seconds, then press the power button.
3. Force a restart. If the iMac seems stuck half on, hold the power button for about ten seconds until everything stops, wait a moment, then press it again.
4. Shine a torch on the screen. If the fans run but the screen is black, darken the room and shine a torch at the glass from an angle. A faint image means the backlight has failed, not the whole iMac.
5. Disconnect everything else. Unplug USB drives, hubs, printers, card readers and Thunderbolt devices, leaving only a keyboard and mouse. A faulty accessory can stop an iMac starting or hang it on the Apple logo.
6. Reset NVRAM. Turn the iMac on and immediately hold Option, Command, P and R together for about 20 seconds. On models that chime you can let go after the second chime; on the 2020 27-inch, let go after the Apple logo appears and disappears for the second time. A wired keyboard is more reliable for startup keys than a wireless one.
7. Try safe mode. If the iMac reaches the Apple logo, restart holding Shift until the login window appears. Safe mode checks the startup disk and loads only essential software. If it starts in safe mode but not normally, suspect software such as a login item or a recently installed app.
8. Try Recovery. Restart holding Command and R, then run First Aid in Disk Utility on the startup disk. If the recovery partition is missing, Option-Command-R starts Internet Recovery on models that support it. Do not erase the disk until your files are safe.
9. Undo recent changes. If you have just fitted RAM to a model with a memory access door, put the original modules back. On 2009–2011 quad-core Core i5 and i7 iMacs, Apple notes the machine will not start if only a single module is installed in any bottom slot, so a half-finished RAM swap can look like a dead iMac.

What the symptoms point to

Flashing question mark folder

The question mark means the iMac cannot find a startup disk it can use. Hold Option at startup to open Startup Manager: if your drive is not listed, it has failed or come loose. On an iMac with its original hard drive that is no surprise. Apple stopped fitting hard drives as standard in August 2020, so most iMac hard drives still in use are six or more years old, and Apple's replacement programs for 1TB Seagate drives in 2009–2011 models and 3TB drives in the Late 2012 27-inch expired long ago. The cure is an SSD upgrade, from $599 with macOS set up and your files moved across if the old drive is readable.

Stuck on the Apple logo or progress bar

A slow or failing hard drive, an interrupted macOS update or a faulty accessory are the common causes. Unplug everything, give a large update plenty of time to finish, then try safe mode and Recovery as above.

One cause is specific to older iMacs. If yours runs a newer macOS installed with OpenCore Legacy Patcher, every macOS update wipes the patcher's root patches, and the patcher's own advice is to switch automatic updates off entirely because a staged update can leave the system broken. If an update has broken a patched iMac, ring us: patching is part of our newer macOS on an old iMac service, from $249.

Turns off by itself or keeps restarting

Heat is the first suspect: dust-clogged fans and heatsinks make an iMac shut itself down to protect itself, especially under sustained load. A thermal service and fan clean costs from $179 on a 2009–2011 iMac, or from $249 on Late 2012 and later models because the glued display must come off. Next is power: a failing power supply can cope at idle and cut out when demand rises. If the iMac restarts and then shows a message that it restarted because of a problem, that is a kernel panic, which can come from software, RAM or the drive, and the report it offers contains useful clues for us.

Fans roaring after a drive replacement

If someone has replaced the hard drive and the fans now run flat out, suspect the drive temperature sensor. On 2009–2010 models the sensor is a cable matched to the drive brand. From 2011, and on 27-inch models from Late 2012 to 2019, Apple's drives report their temperature through custom firmware that retail drives lack, so the fans run at full speed and Apple's hardware test reports a failure. The fix is the right sensor or adapter, not a new fan.

The 2009–2011 diagnostic LEDs

The 2009–2011 aluminium iMacs have diagnostic LEDs on the logic board. LED 1 shows trickle power from the power supply: it should glow any time the power cable is connected, whether or not the iMac is switched on. If it is off with a working cable and outlet, the power supply is the usual diagnosis, which means a repair from $399 (21.5-inch) or from $479 (27-inch) rather than a new logic board. We check it as part of the bench diagnostic. More on these models is on our 2009–2011 iMac page.

When to stop and bring it in

• You smelled burning, heard a pop, or the iMac died during a storm. Leave it unplugged.
• Liquid has been spilled on or into it. Do not power it on to check.
• The drive is clicking, grinding or repeatedly spinning up and stopping. Every attempt to start it puts your files at more risk.
• The checks point to the power supply, logic board, graphics or backlight. None of those are owner repairs: the power supply works at mains voltage, and from Late 2012 the glued display must be cut away before anything inside can be reached.
• You have done the checks twice with no change. A third round will not change the answer.

Call 0400 454 859

What the repair is likely to cost

All prices include GST and a 12-month warranty on parts and labour, and the phone quote is free. Whether a repair is worth it depends on the model: a board repair from $449 makes sense on a 2019 27-inch worth about $800 privately, and much less on a 2011 27-inch worth $60–$150. On the 2020 27-inch, the only Intel iMac on macOS Tahoe, a power supply or board repair is usually the better choice over a new $2,399 M4 iMac. Our logic board, graphics and power supply repair and iMac screen replacement pages explain those jobs, iMac repair costs lists every price, and repair or replace an old iMac helps with the decision. For upgrades as well as repairs, start at iMac repair and upgrades.

Get your data off first

If the iMac holds photos or documents that exist nowhere else, make the data the priority, before any repair and before any attempt to erase and reinstall. On every Intel iMac up to 2019 the drive is separate from the logic board, so a dead board or power supply does not mean lost files, and if the drive is readable we can copy everything off, from $249. From Late 2012 on, the drive sits behind the glued display, so this is a job for the bench, not the kitchen table. The 2020 27-inch is the exception: its SSD is soldered to the logic board, so the board has to work, or be repaired, before the data can be read (see our 27-inch 5K 2019–2020 page). Our data recovery page has the detail.

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Questions

Why does my iMac turn on but the screen stays black?

If the fans spin or it chimes but the screen stays black, the iMac is running and the fault is in the picture path: the backlight, the display, the graphics or the logic board. With the lights off, hold a torch close to the screen: if you can just make out the desktop, the backlight is the likely culprit. On a Mid 2011 27-inch with a Radeon HD 6970M, a black screen is a known symptom of graphics card failure.

Does unplugging an iMac reset the SMC?

On an Intel iMac, yes, when it is done properly. Apple's method is to shut the iMac down, unplug the power cable, wait 15 seconds, plug it back in, wait five seconds and then press the power button. Pulling the plug for a moment and pushing it straight back in is not the same thing. It is harmless and worth doing before anything else.

Can a power surge stop an iMac turning on?

Yes. A surge from a storm or a faulty appliance can take out the power supply, and sometimes the logic board as well. If your iMac died during a storm or when something else on the same circuit failed, leave it unplugged and tell us when you ring. A power supply replacement is from $399 on the 21.5-inch and from $479 on the 27-inch.

Is it worth fixing an iMac that won't turn on?

It depends on the model and the fault. A new power supply, from $399 or from $479 depending on size, or a board repair from $449, is clearly worth it on a 2019 or 2020 27-inch worth $800 to $1,000 privately, but only borderline on a 2017, where it costs about what the machine would sell for. On a 2011 or 2012–2013 27-inch worth a few hundred dollars at most, it only makes sense if you want to keep that particular machine.

Will I lose my files if my iMac won't start?

Usually not. On every Intel iMac from 2009 to 2019 the files are on a separate drive, which survives a failed power supply or logic board. The real risks are a failing hard drive, which gets worse each time you try to start it, and erasing the disk in Recovery. On the 2020 27-inch the SSD is on the logic board, so the board must work first.

How do I get files off an iMac that won't boot?

If the iMac reaches macOS Recovery, you can sometimes copy files to an external drive from there. Target Disk Mode, started by holding T at startup, lets another Mac read the iMac's drive over a Thunderbolt or FireWire cable on models that support it. If neither works, the drive can be read on the bench; with a readable drive, data recovery is from $249.