This problem probably fears everyone who uses a computer: A hard disk with important data is connected and it happens…. nothing. The Mac simply doesn’t want to find or address the drive. This can have a number of causes, which you should check in order. If you are unlucky, the data is gone – but that is only the very last consequence. We will help you with troubleshooting. First, however, you should see what happens when you connect the hard disk to your Mac:
What Happens?
First, connect the hard drive to your Mac. Hard disks and USB sticks usually have small LEDs that indicate the operating status. In addition, with mechanical hard disks you can hear whether the device is running. Pay attention to whether the LED lights up or flashes. If nothing happens at all, i.e. no glowing or flashing and no noise, there are four possible causes:
- The power supply is too weak.
- The Mac USB port is out of order.
- The cable is broken.
- The hard disk is defective.
Hard Drive Not Recognized? The Hardware Troubleshooting Guide
To check what the problem is, you should first perform the following steps to diagnose the problem:
- First disconnect all other USB and Thunderbolt devices from your Mac to rule out sources of error.
- If you have a Macbook (Pro), you should also make sure there is enough power at the USB port: connect the notebook to the power supply.
- Now restart the Mac once.
- If the hard drive has its own power supply, connect it to the power supply as well.
- Check that the cable is correctly connected to the hard drive.
- Then connect the hard drive to your Mac.
- If that doesn’t change anything, you will need to connect the hard drive to another USB port on your Mac. Avoid hubs or adapters when doing this to reduce possible sources of errors.
- If still nothing happens, you should connect the hard drive to another PC or Mac. If it works here, it’s your Mac’s fault: There might be an error in the USB controller.
- If the LED does not light up on the other PC either, there are still two possibilities: Either the cable is defective – or the hard drive.
- Use another cable. If nothing happens, the hard disk is probably broken.
Hard Drive Not Recognized? The Software Troubleshooting Guide
If the LED of the hard disk or USB stick lights up and a hardware defect can be excluded, the power supply is available. If it flashes briefly, the Mac has also addressed it. If it is still not displayed, there may be a software error:
- Restart the Mac and check if the hard disk is mounted afterwards.
- To do this, open a Finder window. The disk should be displayed here.
- If it doesn’t, open Disk Utility from /Applications/Utilities/ and see if the disk shows up here.
- Click on the hard disk. It may not be formatted correctly. MacOS can read many hard disk formats, but not all of them (like Linux).
- Format the hard disk with the "Erase" button. Attention: All data on the disk will be lost!
- Use the following settings for hard disks that you only use for macOS: Format: Mac OS Extended (journaled) and Scheme: GUID.
- For hard disks that you want to use for exchange with Windows use the format: ExFAT and the scheme: Master Boot Record.
- After that click on "Delete". After that you should be able to use the hard disk.
- If an error message appears during formatting, the hard disk is probably defective. Replace it.