Original post by: Josh ,
Cesar, The lock you're talking about is the firmware password. You'll need to find out how much RAM was in the machine when you got it... and replace the RAM with the same, exact amount of compatible RAM. That's the only way to reset the firmware password. Once you have the password reset, you'll be able to boot to other drives and begin troubleshooting the issue more. If you can't get the password reset, you'll need to take it into an Apple Store or a repair center to have them do it. You'll be able to find out a lot more about the situation when you can boot from an external and run some more tests.