Hello, Please follow this :
Shut down your computer and remove the battery.
Locate your RAM, remove one of the RAM modules and put it aside.
Put the battery in, and boot your computer while holding the Command + Option + P + R keys to reset the parameter RAM.
Wait for the chime to sound three times.
Release the keys and shut down the computer.
Remove the battery again, and reinsert the RAM module.
Put the battery back in.
Boot up your Mac, and you should not see the firmware lock again.
