Quick Answers
If your Mac won’t reinstall the operating system, here are some quick things to try:
- Restart your Mac and try reinstalling again
- Make sure you have a good internet connection and sufficient disk space
- Try reinstalling from macOS Recovery instead of the installer app
- Reset NVRAM before reinstalling
- Try a different USB port if installing from a bootable installer
Reinstalling the Mac operating system is often necessary to fix software issues, upgrade to a newer OS version, or wipe your Mac and start fresh. However, sometimes the reinstall process doesn’t go as planned and ends up failing or getting stuck.
A failed or incomplete macOS install can be incredibly frustrating. You might see error messages, get stuck on a progress bar, or boot to a prohibitory sign or flashing question mark folder. Whatever the specifics, if your Mac won’t reinstall macOS properly, you’ll need to troubleshoot and resolve the problem before you can use your Mac again.
In this guide, I’ll cover the most common reasons why a Mac won’t reinstall, along with steps to fix macOS reinstallation problems. We’ll look at general troubleshooting tips, recovery mode options, and tools like macOS Utilities. Follow along and hopefully you’ll get your Mac back up and running with macOS installed correctly.
Why Your Mac Won’t Reinstall macOS
There are a number of potential culprits when a Mac reinstallation goes wrong or gets stuck:
Network connection issues
The macOS installer requires an internet connection to download necessary components and verify your Apple ID. Connection problems like a weak Wi-Fi signal, misconfigured network, or server issues can disrupt the download and cause the install to fail.
Not enough storage space
Reinstalling macOS takes up a significant amount of storage space on your Mac. You’ll typically need at least 12-15GB of available space on your startup disk to complete the installation. Insufficient disk space can halt the install.
Incompatible or damaged USB installer
If you’re installing macOS from a bootable USB drive and run into problems, the USB itself could be to blame. Using an incompatible drive format, corrupted installer app, or physical USB damage can all block the reinstallation.
NVRAM issues
The NVRAM stores low-level settings that macOS needs to boot and function correctly. Corrupted NVRAM could prevent your Mac from booting to the installer and completing the reinstall process.
Startup drive problems
Your Mac’s built-in startup drive has to be healthy for macOS to be installed properly. Drive errors, filesystem damage, partition issues and stuck firmware passwords can all interfere with reinstallation.
Incompatible OS version
Trying to install an OS version that isn’t designed for your Mac model, like an older OS or beta/developer-only version, is a recipe for installation failure or getting stuck on boot screens.
Buggy installer app
Sometimes the macOS installer application itself is the culprit. Corrupted installer files, bugs in the installer, and conflicts with other apps on your Mac could all cause the reinstall process to go sideways.
Finding the exact cause typically involves testing and troubleshooting until you isolate the problem. Fortunately, there are solutions for all of these potential issues – keep reading for specific steps to get your Mac reinstallation back on track.
General Troubleshooting Tips
Before digging into more advanced troubleshooting, here are some basic steps to try first when your Mac won’t reinstall:
Restart your Mac
If the install process is stuck, one of the simplest fixes is to restart your Mac and try again. Power it down completely, wait a few minutes, then restart and launch the macOS installer again.
Check network connection
Make sure your Mac has a strong Wi-Fi or ethernet connection to download the full installer. Try disconnecting and reconnecting to the network before starting the install.
Free up disk space
Delete unused apps, files and iOS device backups to ensure you have at least 12-15GB of free space on your startup drive before attempting to reinstall.
Use wired connection
Wi-Fi issues are common during installation. For a more reliable connection, connect your Mac directly to a router or modem with an ethernet cable.
Try safe mode
Booting to safe mode can isolate software issues and allow the reinstall to proceed. Restart your Mac and hold Shift after the startup chime to enter safe mode.
Check USB connection
If installing from a bootable USB drive, connect it to a different port and use a high-quality USB 3 cable to ensure a good connection.
Disable anti-virus software
Anti-virus tools like Avast and Norton can sometimes interfere with the macOS installer. Temporarily disabling your anti-virus may help.
Use the latest installer
Download the newest macOS installer from the App Store or Apple Support website to avoid bugs in older versions of the installer application.
Reset NVRAM
Resetting your Mac’s NVRAM can clear out low-level settings that may be preventing macOS from installing correctly.
How to reset NVRAM
Follow these steps to reset NVRAM on your Mac:
- Shut down your Mac completely.
- Press the power button and immediately hold down Command + Option + P + R keys together.
- Keep holding the four keys until you hear the startup chime a second time.
- Release the keys and let your Mac finish booting up.
Now when you attempt the OS reinstallation, NVRAM issues should be cleared out of the way.
Start up in Recovery Mode
The macOS Recovery environment on your built-in drive can be used to reinstall the OS without needing the standard installer app.
How to reinstall macOS from Recovery
Follow these steps to reinstall the OS using Recovery mode:
- Restart your Mac and hold down Command + R immediately after you see the Apple logo.
- This will boot your Mac into Recovery mode once the progress bar finishes.
- Click Reinstall macOS from the Recovery mode menu.
- Follow the on-screen prompts to reinstall the latest macOS version.
Because Recovery mode installs macOS directly from Apple’s servers instead of a local file, this approach may succeed if the normal installer was having issues.
Boot to Apple Diagnostics
Apple Diagnostics can check your Mac hardware for underlying problems that may be preventing reinstallation.
How to use Apple Diagnostics
- Restart your Mac while holding D.
- This will load the diagnostic tool from its hidden partition.
- Follow the on-screen instructions and check for any hardware-related issues reported after diagnostics finish.
Diagnosing and fixing drive corruption, RAM issues, or temperature problems may allow macOS to install correctly after restarting.
Erase and Format the Startup Drive
Wiping your Mac’s boot drive erases any filesystem damage and prepares it for reinstallation.
How to erase the startup drive
- Boot to Recovery mode by holding Command + R at startup.
- Select Disk Utility from the Recovery menu.
- Choose your startup drive in the sidebar.
- Click Erase at the top. Give it a name and format, then click Erase.
With your Mac’s main drive wiped clean, you can quit Disk Utility and proceed to reinstall macOS in Recovery mode.
Create a Bootable USB Installer
If your Mac won’t boot to the installer app on the built-in drive, creating an external bootable installer on a USB drive offers a handy alternative.
How to make a bootable installer
- Get a USB drive that’s at least 8GB in capacity.
- Format the drive using Disk Utility to the MacOS Extended format.
- Download the macOS installer app from the App Store onto your Mac.
- Run the createinstallmedia command in Terminal to copy the installer to the USB drive.
- Boot your Mac from the USB drive and install macOS from there.
With macOS installed cleanly from the external drive, you can troubleshoot why the internal drive installer wasn’t working properly.
Check Drive Partition Map Scheme
An unsupported partition scheme on your startup drive may be preventing macOS from installing properly.
How to check partition scheme
- Boot to Recovery mode and open Disk Utility.
- Select your startup drive and click Info.
- Check the Partition Map Scheme entry.
- If it says MBR instead of GPT, the drive will need to be erased and partitioned correctly.
GPT partitioned drives work best for Boot Camp and macOS installation compared to the MBR format.
Conclusion
Troubleshooting a Mac that won’t reinstall macOS can be frustrating, but using the right tools and techniques will get your Mac back up and running. Start with general fixes like restarting, freeing disk space, redownloading the installer, and verifying network connections. If those don’t work, booting to Recovery mode, Apple Diagnostics, or an external USB drive can often successfully reinstall macOS when other options fail. In the worst case, erasing your startup drive entirely gives you a blank slate to start fresh.
Back up your important files, have your Wi-Fi password handy, and set aside plenty of time when tackling a difficult macOS reinstallation. Stay patient and methodical in applying these troubleshooting tips, and your Mac should eventually have a smooth, successful OS reinstall process.
| Issue | Potential solutions |
|---|---|
| Network connection issues |
|
| Not enough disk space |
|
| USB installer problems |
|
| macOS version incompatible |
|