Diagnose problems with your Mac
Apple Diagnostics and Apple Hardware Test are tools 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 or Apple Hardware Test, even if it doesn’t start using macOS.
The tool you use depends on your Mac model and macOS version. To see the model and version, choose Apple menu 
> About This Mac.
If your Mac is from 2013 or later, use Apple Diagnostics, which is built into your Mac.
If your Mac is from 2012 or earlier and has OS X 10.8.4 or later, use Apple Hardware Test, which is built into your Mac.
If your Mac is from 2012 or earlier and has OS X 10.8.3 or earlier, use the system software disc or USB flash drive that came with your Mac.
Use Apple Diagnostics
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 web page 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 Authorised Service Provider.
To change the language again, press Command-L.
Use Apple Hardware Test
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.When the Apple Hardware Test chooser screen appears, select the language you want to use, then press the Return key or click the right arrow button.
If you don’t see the chooser screen, Apple Hardware Test may not be available on your Mac. You may be able to start Apple Hardware Test from the internet. Reconnect your Mac to the network, then restart your Mac while pressing and holding both the Option and D keys.
When the Apple Hardware Test main screen appears, follow the onscreen instructions.
If Apple Hardware Test detects a problem, an alert message appears. Make a note of the message to use if you need to call Apple Support.
Use a system software disc or USB flash drive
If your Mac came with a system software disc or USB flash drive, you may be able to use it to start Apple Hardware Test.
Important: Follow these instructions only if your Mac came with a system software disc or USB flash drive. Do not try to use a disc or USB flash drive from another Mac model.
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.
Insert the system software disc or USB flash drive.
On your Mac, choose Apple menu
> Restart, then press and hold the D key while your Mac restarts.When the Apple Hardware Test chooser screen appears, select the language you want to use, then press the Return key or click the right arrow button.
When the Apple Hardware Test main screen appears, follow the onscreen instructions.
If Apple Hardware Test detects a problem, an alert message appears. Make a note of the message to use if you need to call Apple Support.
Apple Diagnostics and Apple Hardware Test don’t check external hardware components, such as USB or FireWire, or non-Apple devices, such as PCI cards from other vendors. They don’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.