How to Reset an EFI Chip
An EFI (extensible firmware interface) is a set of instructions stored in computer memory that act as an interface between computer components and the operating system during startup. If you are having startup problems or your computer components do not work properly, you may be able to solve the problem by resetting the EFI to its default settings. The EFI standard is most widely used in Intel-based Macintosh computers, although other computer manufacturers are beginning to replace the older BIOS (Basic Input/Output System) firmware with EFI. This article pertains to Macintosh computers.
Shut down the computer.
Turn on the computer and immediately hold down the "Command," "Option," "P" and "R" keys at the same time.
Release the keys after you hear the computer beep a second time.
Check to see if the computer is operating properly. If not, continue through the next steps.
Reboot the computer and hold down the "Command," "Option," "O" and "F" keys at the same time during startup.
Wait until you see the message "To continue booting, type 'mac-boot' and press return." If the message does not appear, try starting the computer by holding down the power button continuously until the message appears.
Type "reset-nvram" and press "Return."
Type "reset-all" and press "Return."