My Mac plays the noise that it is on but the screen is black. What does that mean?

Try adjusting the screen brightness, but sometimes this is not possible until after logging into the laptop.

Connect an external display. With the charger, keyboard & mouse connected as well, close the lid to see if the video will go to the external display so you can try logging in. You can also try to log in blindly by waiting long enough for the laptop to reach the login screen, then type the first character of one of the user accounts followed by pressing the "Return" key. Then enter the password for that user account and again press the "Return" key in order to submit the password. Hopefully this will allow you to log in so that the external display gets a video signal so you can interact with the laptop. If this works, then it means the laptop's built-in Display Assembly is most likely bad which will require a repair by Apple or an Apple Authorized Service Provider.

FYI, make sure the Caps Lock key is not enabled when typing the password.

You can also try forcing a power off by holding the power button, but first press the Caps Lock key so that its LED is lit. When the Caps Lock LED goes dark, then the laptop has been powered off. Then try powering on the laptop and try using the external display and/or blind login.