If you are having an issue with your Macbook air/Pro hanging on boot up please do the following:
PRAM RESET
- Shut down the computer.
- Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step
- Turn on the computer.
- Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
- Hold the keys down until the computer restarts and you hear the startup sound for the second time.
- Release the keys.
For the full webpage please visit the below site: