Troubleshooting the Unbootable Mac Error: A Folder with a Flashing Question Mark at Startup  

software or upgrade to a newer Mac OS
software or upgrade to a newer Mac OS

A folder with a flashing question mark at startup with a black background means the startup disk is not available or there is no working Mac OS for startup.  

 But why does this happen?   

The common reasons and the solutions will be explained below. If you don’t know what has cause the trouble, try the solutions in sequence.  

Did you replace a new SSD? 

If you just replaced a new SSD for better performance or larger storage, the reason for the error could possibly be a faulty connection during the replacement. The faulty or poor connection may result in the Mac computer no longer recognizing the startup disk.  

To solve the problem, you need to open up the Mac computer again to check all connections. After that, you can try to reboot the computer normally.  

Did you boot up the Mac from an external drive before? 

For testing or other purposes, some people may need to boot up their Mac from an external drive which contains a Mac OS. When the Mac is turning on next time and it may try to find the external drive to boot from, but the external drive is detached. As a result, the Mac shows up a folder with a flashing question mark telling it can’t find the bootup disk.  

To solve the problem, what you need to do is to reboot the Mac and press down Command + R instantly before Mac boots up. Then wait until the Mac boot into Recovery, click on Apple logo and choose Startup Disk. Then select the drive which contains the Mac OS. 

Are there other operating systems like Windows or Linux on the startup disk? 

If you installed any non-Mac operating system on the startup disk, the Mac may be confused when it is reading the disk at startup. Therefore, the Mac will display an error to tell you that it can’t find a working Mac OS.  
To boot up the Mac successfully, you need to manually help select the Mac OS. Reboot the Mac and Press down Option key immediately before the Mac starts up. Then you will see available operating systems from which you can choose the one you want to boot up with.   

Did you recently update the software or upgrade to a newer Mac OS? 
 

Software updates or system upgrade is another common reason for this non-booting Mac error, because the updates or upgrade may corrupt the system files and then leave the Mac’s hard drive unrecognized or unreadable.  

There are two ways to make the Mac boot again:  

  • Restore From Time Machine Backup. If you have been using Time Machine to back up the Mac, it will be very easy for you to roll back the Mac to a previous state. Choose Restore From Time Machine after you boot into Recovery Mode by pressing down Command + R before restarting. Attach the backup drive to the Mac and follow the wizard to select an item to restore the Mac.  
  • Reinstall macOS/OS X. Now that the startup disk is corrupted and you don’t have a Time Machine backup, you can format the startup disk and reinstall macOS/OS X to fix the problem. It is recommended that you format the disk in Disk Utility using Erase first and then reinstall the OS, because it will reduce the possibility of failure in reinstallation.  

Warning: the two methods may cause permanent data loss, so get the important files off the unbootable Mac ahead of time by using target disk mode or data recovery software.   

Has the startup disk been physically damaged?  

Did you hear clicking, humming, beeping or any other noises when the computer is turning on? Did you ever drop the computer hard on ground? If you did, the chances are that the startup disk has been physically damaged and the startup disk is completely unrecognizable. Even worse, when you try to reboot the Mac, the Mac computer no longer turns on. It is beyond any repair by yourself in this situation.  

You can go to a local Apple store to see if they can help restore the Mac files or replace a new SSD on your Mac.  

Conclusion   

When the Mac starts at a folder with a flashing question mark, it could be something easy to fix like a corrupted startup disk or poor connection of hard drive to the Mac, but it could be something beyond fixing. While you are following the solutions, don’t forget to keep your files safe.  

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