Press the power button 
on your Mac, then check for signs of power such as these:
- Sounds, such as from a fan, hard disk, or other startup sound
- Lights, such as from a backlit keyboard, Caps Lock key, or sleep indicator light
If your Mac has no signs of power, start by making sure that it's receiving power:
- Make sure that your power cable is undamaged and securely plugged into your Mac and a working electrical outlet. If you're not sure about the outlet, test it with a lamp or other device.
- If you're using a Mac notebook, make sure that you're using the correct power cable and adapter, and leave them plugged in long enough to provide a usable battery charge. Learn how to troubleshoot MagSafe power adapters or USB-C power adapters.
Then try these solutions, whether or not your Mac has signs of power:
- Press and hold the power button for 10 seconds, then press it again. If that doesn't help, repeat after unplugging accessories from your Mac, including printers, drives, USB hubs, and mobile devices. (You could have an issue with one or more of those devices or their cables.)
- If nothing appears on your display, make sure that its brightness is turned up. Mac notebook computers have a Brightness Up
key on the built-in keyboard. If you're using an external display, make sure that it's turned on and isn't experiencing any other issues. - Reset the System Management Controller (SMC).
If your Mac turns on but doesn't finish starting up, one of these solutions might help. If you need to turn off your Mac first, press and hold the power button for 10 seconds.
- If your Mac starts up to a question mark, circle with a line through it, or something other than your desktop, learn about the screens your Mac displays as it starts up.
- Start up in safe mode.
- Reset NVRAM.
- If the issue occurs after logging in to your user account, test the issue by logging in to another account, if available.
- Start up from macOS Recovery. If the only way that you can start up is from macOS Recovery, the operating system on your startup disk might no longer be usable. In that case, reinstall macOS or restore from a backup.
- If you recently installed memory or a hard disk (or SSD), make sure that it's compatible and installed correctly. If possible, remove it and test with the original memory or disk.
If your Mac still doesn't turn or start up, or you can't successfully reinstall macOS or restore from a backup, contact Apple Support, an Apple Store, or an Apple Authorized Service Provider. Meanwhile, if your Mac doesn't finish starting up and you have another startup disk, you might be able to connect it to your Mac and start up from that disk instead of your current startup disk.