If your Mac doesn’t turn on
If your computer won’t turn on, make sure you plugged it in and installed any new memory correctly.
Check power and cables: Make sure the power cable is plugged into the computer and into a functioning power outlet. On portable computers, the power adapter plug glows amber if the battery is being charged, and glows green when the battery is fully charged. Be sure to use the power adapter that came with your computer or a compatible replacement adapter.
If that doesn’t work, try another power cable or power adapter to test whether the problem is with the power supply or the computer itself.
If you have a portable Mac with a removable battery: You can check if your battery needs to be recharged by pressing the small button on the battery or on the side of your computer. See your computer’s documentation to find out where the button is. You should see lights indicating the battery’s level of charge. If only one battery indicator light is flashing, allow the power adapter to charge the battery until at least one indicator light is glowing continuously.
If you still can’t start up your Mac, it may need to be serviced. See Find out how to service or repair your Mac.