1. Power off your MacBook.
2. Hold down the power button.
3. Before the grey screen appears, press the Command, Option, P, and R keys at the same time.
4. Hold these keys until your Macbook restarts and you hear the startup sound a second time.
5. Release the keys.
Keep in mind that you are going to have to reset a few things, such as the time, but it's not a big deal to do.