How to unlock a disabled MacBook with a locked screen?

If your Mac is using a firmware password, the lock icon appears when you try to start up from another disk or volume, such as an external drive or macOS Recovery.

If you can't remember your firmware password, schedule an in-person service appointment with an Apple Store or Apple Authorized Service Provider. Bring your Mac and its original receipt or invoice as proof of purchase.

My car won't go. Help.

Please provide more details about your problem. In the meantime, perhaps one of these will help.

If your Mac doesn't turn on - Apple Support

If your Mac starts up to a blank screen - Apple Support