Diagnose problems with your Mac
Apple Diagnostics is a tool you can use to diagnose problems with your computer’s internal hardware, such as the logic board, memory, and wireless components. You may be able to start your Mac with Apple Diagnostics, even if it doesn’t start using macOS.
Print these instructions: Click the Share button in the Help window, then choose Print.
Disconnect all external devices except the keyboard, mouse, display, and speakers. If you have an Ethernet cable or external DVD drive, disconnect it.
On your Mac, choose Apple menu > Restart, then press and hold the D key while your Mac restarts. Keep holding the D key until the screen listing different languages appears.
Select a language. Apple Diagnostics starts automatically.
When Apple Diagnostics is finished, it lists any problems it finds. (The reference code is for use by Apple Support.)
Follow the onscreen instructions.
To start your Mac from the built-in recovery disk and open the Contact Apple Support webpage in Safari, click “Get started.”
If Apple Diagnostics reports that your Wi-Fi card is not working properly, contact Apple Support or take your Mac to an Apple Store or Apple Authorized Service Provider.
To change the language again, press Command-L.
Apple Diagnostics doesn’t check external hardware components, such as USB, or non-Apple devices, such as PCI cards from other vendors. It doesn’t check for operating system (macOS) or software-related problems such as app or extension conflicts.
If a hardware problem isn’t detected, there may be a problem with the version of macOS you’re using and you may need to reinstall it. See Reinstall macOS.