The SMC is the System Management Controller. If not, the MacBook Pro will still fail to start, and you’ll need to keep reading. If you’re fortunate, it will boot successfully. Once you have held the power button down, leave it a few seconds and then press it again to start the MacBook Pro as normal. This action cuts all power to the laptop and is the equivalent of removing the battery. All you need to do is hold down the power button for a minimum of ten seconds. While it sounds involved, it is very straightforward. The next step involves performing a complete power cycle of your MacBook Pro.