When I boot up my system I get a pad lock symbol

Here's a good Apple T/N which explains the different boot up symbols: About the screens you see when your Mac starts up.

So as you can see your system has a firmware password set. Here's more on that: Use a firmware password on your Mac.

If you didn't set it you'll need to find the person who did, or if you bought the system used you'll need to go back to the person who sold you the system (the owner) and have him release the iCloud lock which appears to have been set. If he can't do it get your money back as it was likely stolen!

Otherwise you'll need to visit an Apple Store with the needed proof you bought the system so they can unlock it if you forgot the password.