iMac won't turn on? Safe checks and likely causes
11 November 2026 · Mac guides
You press the power button on your iMac and nothing happens. Or something seems to happen, but the screen stays black. Both feel the same at the time, but they point to different faults, and working out which one you have is the most useful first step. This guide covers the safe checks you can do at home, what the usual causes are, and how to keep your files safe while you sort it out.
First: is it dead, or just dark?
Before anything else, look and listen for signs of life when you press the power button:
- Does the fan or the hard drive make any noise, even briefly?
- Do you hear a startup sound?
- On a wired keyboard, does the Caps Lock light come on when you press it?
- If you shine a torch closely at the screen, can you make out a faint image?
If the answer to all of these is no, the iMac is probably not getting power or not starting at all. If any of them is yes, the iMac may be running but not showing a picture, which is more often a display, backlight or graphics problem. In that case our guide to iMac repair covers the screen faults we see.
Safe checks for an iMac with no power
Check the cable and the socket
It sounds obvious, but it catches people out. Try a different wall socket, not just a different socket on the same extension lead. Make sure the plug is fully home at the back of the iMac: on Intel iMacs the power cable goes straight into the machine and can work loose if the iMac has been moved. If you have a spare kettle-style cable of the same type, try that too.
The 24-inch Apple silicon iMacs use a separate power adapter with a magnetic connector on the back. Check that the connector snaps firmly into place, that the cable is not kinked or damaged, and that the adapter is plugged directly into the wall. Some of these adapters also have an Ethernet port, which is a reminder that the adapter itself can fail like any other part.
Try a longer press
Hold the power button for about ten seconds, let go, wait a few seconds, then press it once normally. If the iMac was frozen in a deep sleep rather than switched off, this can bring it back.
Reset the power controller on an Intel iMac
Intel iMacs have a system management controller that looks after power. Resetting it is safe and does not touch your files. Shut down if you can, unplug the power cable, wait about 15 seconds, plug it back in, wait another five seconds, then press the power button. Apple silicon iMacs do not have this controller, so unplugging the adapter for a minute and trying again is the nearest equivalent.
Unplug everything else
Disconnect all USB devices, drives, hubs and displays, leaving only the power cable. A faulty accessory or a short in a cable can occasionally stop a Mac from starting.
What usually causes it
Power supply
On Intel iMacs the power supply is inside the machine. It is one of the more common reasons an older iMac goes completely dead, sometimes after a power cut or a storm, sometimes simply through age. A clicking sound when you plug it in, or an iMac that only starts after several tries, can be early warning signs.
Logic board
If the power supply is fine, the fault is often on the logic board: a failed component in the power circuitry, damage from a spill, or corrosion. People are often told the whole board needs replacing, but many of these faults can be fixed at component level. We carry out chip-level logic board repair, which means repairing the faulty part rather than swapping the whole board.
Power button or software
Less often, the power button itself has failed, or the iMac is actually starting but is stuck because of a failed update. These are usually quicker to sort out once diagnosed.
What not to do
- Do not open the back of an Intel iMac to look at the power supply. It runs on mains voltage and parts of it can hold a charge after unplugging.
- Do not keep switching it on and off repeatedly. If there is a short, repeated attempts can make things worse.
- Do not erase or reinstall anything if it does eventually start. Back up first.
Keeping your files safe
If your files are backed up to Time Machine or iCloud, a dead iMac is a repair problem. If they are not, it is also a data problem, and the order of work matters.
On many older Intel iMacs, the drive can be taken out and read separately if the machine cannot be fixed. On newer Intel iMacs with Apple's T2 security chip, and on all Apple silicon iMacs, the storage is encrypted and tied to the logic board, so in practice getting your files back depends on getting the board working. That is one more reason to choose a repair that fixes the original board where possible. If your files matter and you have no backup, ask about our free assessment for Mac data recovery before anyone replaces parts.
Repair or replace?
If your iMac is a recent model, a power fault is almost always worth fixing. If it is very old and no longer gets macOS updates, it is worth weighing up whether to repair it or simply recover your files and move on. We will give you an honest view either way. An iMac is heavy and awkward to carry, so in London our bike collection can save you the trip.
Get a quote
If your iMac will not turn on, call 020 7394 2525 or bring it to 80 Willow Walk, London SE1 5SY. We are open 9am to 6pm, Monday to Saturday, with bike collection in London and courier collection across the UK.