Help! My MacBook Pro’s screen remains black

Try booting from the Recovery HD:

Boot from the Recovery HD

1. Restart the computer.
2. Immediately, at or before the chime, press and hold down the "COMMAND" and "R" keys together.
3. Release the keys when the Apple logo and progress bar appear.
4. Upon completion the Utility Menu should appear.

If all works doing the above, then you should do the following:

Reinstall El Capitan or Later Without Erasing Drive

1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
2. Select Disk Utility and click on the Continue button.
3. Select the indented (usually, Macintosh HD) volume entry from the side list.
4. Click on the First Aid button in Disk Utility's toolbar. Wait until the Done button activates, then click on it.
5. Quit Disk Utility and return to the Utility Menu.
6. Select Install OS X and click on the Continue button.

If the computer still doesn't have a normal display, then you will need to take it in for repair. Make an appointment at the Apple Genius Bar for service. If you need to find an Apple Store - Find a Store - Apple. Also, see How to find your nearest Apple Authorized Service Provider (AASP) or Distributor (AAD).