What resetting your iMac means and which method you need

Resetting an iMac is not one thing — it depends on what problem you are solving. A restart closes everything and boots fresh, which fixes most freezes and slow performance. A factory reset erases your entire drive and reinstalls macOS from scratch, which you do when selling the machine or fixing deep software corruption. A password reset lets you back in if you have forgotten your login. A SMC reset fixes hardware issues like fans running constantly or the machine not waking from sleep. Most people need a restart first; if that does not work, you move to the next step.

This guide walks you through each method in order of how often you will actually need it. Start with the simplest — a restart — and move down only if the problem persists.

Key Takeaways

  • A straightforward restart fixes most iMac problems and takes two minutes; hold the power button for ten seconds if the machine is frozen.
  • A factory reset erases everything and reinstalls macOS, which you do before selling or when software corruption is severe; back up your files first.
  • You can reset a forgotten password from the login screen without erasing anything, using your Apple ID or a recovery key.
  • An SMC reset fixes hardware issues like stuck fans or sleep problems and requires holding specific key combinations during startup.
  • Recovery Mode (Command-R at startup) is the gateway to all major resets and lets you reinstall macOS without losing your files.

Restart your iMac the normal way

Click the Apple menu in the top left corner, then select Restart. A dialog box appears asking you to confirm. Click Restart again. The machine shuts down, waits a few seconds, and boots back up. This usually takes two to three minutes. Any frozen programs close, temporary files clear, and the system starts fresh.

If your iMac is completely frozen and will not respond to clicks or keyboard input, hold the power button (on the back of the machine, or on the keyboard) for ten seconds. The screen goes black. Wait five seconds, then press the power button again to turn it back on. This is a forced shutdown and should be your last resort because it can corrupt files if something was writing to the drive, but it works when nothing else does.

Force quit a frozen program without restarting

If only one program is frozen and the rest of your iMac is responsive, you do not need to restart the whole machine. Press Command + Option + Esc at the same time. A window titled "Force Quit Applications" appears, showing all open programs. Click the frozen program to highlight it, then click the Force Quit button. The program closes when ready. You can then reopen it or continue working.

This is faster than a full restart and safer because other programs stay open and unsaved work in other windows is not lost. Use it whenever a single app is stuck but the rest of the system is working.

Reset your password from the login screen

If you have forgotten your login password, you do not need to erase the machine. At the login screen, click the question mark icon below the password field (or look for a "Reset Password" option, depending on your macOS version). A new window opens asking how you want to reset it.

If you remember your Apple ID and password, select that option and follow the prompts. If you have a recovery key from setting up two-factor authentication, you can use that instead. If you have neither, you will need to use another administrator account on the machine, or you will need to erase and reinstall macOS. The password reset does not touch your files — only your login credentials change.

Perform a factory reset by erasing and reinstalling macOS

A factory reset wipes your entire drive and reinstalls macOS as if the machine were brand new. Do this only if you are selling the iMac, giving it away, or the software is so corrupted that nothing else works. Back up all your files first — this process destroys everything on the drive.

Start by restarting your iMac and holding Command + R as soon as you hear the startup sound or see the Apple logo. Keep holding until you see a spinning globe or the macOS Utilities window. This boots into Recovery Mode. Click Disk Utility, then select your main drive (usually called "Macintosh HD" or similar) from the list on the left. Click the Erase button at the top. A dialog appears asking for a name and format — leave the name as is and make sure the format is APFS (or Mac OS Extended if your iMac is very old). Click Erase again. The drive is now blank.

Close Disk Utility and you are back at the Utilities window. Click Reinstall macOS (or "Install macOS" depending on your version). Follow the on-screen prompts. The installer downloads the correct version of macOS for your iMac and installs it. This takes 20 to 45 minutes depending on your internet speed and how old the machine is. When it finishes, your iMac boots into the setup screen as if it were new out of the box.

Reset the SMC to fix hardware and power issues

The SMC (System Management Controller) handles power, fans, sleep, and thermal management. If your iMac's fans are running constantly, it will not wake from sleep, the power button does not work, or the machine shuts down unexpectedly, an SMC reset often fixes it.

The steps depend on whether your iMac has an Apple Silicon chip (M1, M2, M3, or newer) or an Intel processor. For Apple Silicon iMacs: shut down the machine completely. Press and hold the power button for ten seconds, then release. Wait a few seconds and press the power button again to turn it back on. That is the entire reset.

For Intel iMacs: shut down the machine. Press and hold Shift + Control + Option (all on the left side of the keyboard) plus the power button at the same time. Hold all four for ten seconds, then release. The screen may flash or the fans may make noise — that is normal. Wait a few seconds, then press the power button to turn the machine back on. The SMC is now reset.

Use Recovery Mode for other reset and repair options

Recovery Mode is the gateway to several other tools. Restart your iMac and hold Command + R until you see the Utilities window. From here you can run Disk Utility to repair your drive (click your main drive, then First Aid, then Run), reinstall macOS without erasing, or restore from a Time Machine backup if you have one.

If you need to erase the drive and reinstall but want to keep your files, use Migration Assistant after the reinstall finishes — it copies your files, programs, and settings from a backup or another Mac. This is slower than a factory reset but safer if you have important data.

Frequently Asked Questions

Will restarting my iMac delete my files?

No. A restart closes all programs and reboots the system, but your files stay on the drive. Only a factory reset (erase and reinstall) deletes files. Always back up before doing a factory reset.

How long does a factory reset take?

The erase takes a few minutes. The macOS reinstall takes 20 to 45 minutes depending on your internet speed and the age of your iMac. Older machines and slower internet connections take longer.

What is the difference between Command-R and Command-Shift-Option-R?

Command-R boots into Recovery Mode using the macOS version that came with your iMac. Command-Shift-Option-R boots into Internet Recovery and downloads the latest compatible macOS version. Use Command-R unless you need the newest version or your drive is too damaged to access local recovery.

Can I undo a factory reset?

No. Once you erase the drive and reinstall macOS, the old files are gone unless you have a backup. Always back up to an external drive or cloud storage before erasing.

My iMac is stuck on the startup screen. What do I do?

Hold the power button for ten seconds to force it off. Wait ten seconds, then press the power button to turn it back on. If it gets stuck again, restart into Recovery Mode (Command-R) and run Disk Utility's First Aid to check for drive errors.