After isolating an issue on your Mac to a possible hardware issue, you can use Apple Diagnostics to help determine which hardware component might be causing the issue. Apple Diagnostics also suggests solutions and helps you contact Apple Support for assistance.

Seagate SeaTools. Works from both inside and outside of Windows. Completely free. The most efficient method might be to boot the Mac into Single User Mode and use the fsck command - a shortcut to launch the file system check feature. First, create a backup and then shut down your computer. To access this mode, press and hold Command.

If your Mac was introduced before June 2013, it uses Apple Hardware Test instead.

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How to use Apple Diagnostics

1. Disconnect all external devices except keyboard, mouse, display, Ethernet connection (if applicable), and connection to AC power.
2. Make sure that your Mac is on a hard, flat, stable surface with good ventilation.
3. Shut down your Mac.
4. Turn on your Mac, then immediately press and hold the D key on your keyboard. Keep holding until you see a screen asking you to choose your language. When Apple Diagnostics knows your language, it displays a progress bar indicating that it's checking your Mac:
   
5. Checking your Mac takes 2 or 3 minutes. If any issues are found, Apple Diagnostics suggests solutions and provides reference codes. Note the reference codes before continuing.
   
6. Choose from these options:
   • To repeat the test, click ”Run the test again” or press Command (⌘)-R.
   • For more information, including details about your service and support options, click ”Get started” or press Command-G.
   • To restart your Mac, click Restart or press R.
   • To shut down, click Shut Down or press S.

If you choose to get more information, your Mac starts up from macOS Recovery and displays a web page asking you to choose your country or region. Click ”Agree to send” to send your serial number and reference codes to Apple. Then follow the onscreen service and support instructions. When you're done, you can choose Restart or Shut Down from the Apple menu.

This step requires an Internet connection. If you're not connected to the Internet, you'll see a page describing how to get connected.

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If holding down the D key at startup doesn't start Apple Diagnostics:

• If you're using a firmware password, turn it off. You can turn it on again after using Apple Diagnostics.
• Hold down Option-D at startup to attempt to start Apple Diagnostics over the Internet.