my macbook has a black screen but the keyboard is lit

The related article mentions a few more things to try, before you have to get it serviced:

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1. Press and hold the power button on your Mac for about 10 seconds.* If your Mac is turned on, this turns it off.
2. Press and release the power button and see if your Mac starts up.
3. If your screen remains blank, press and hold the power button for about 10 seconds again to make sure that your Mac is turned off.
4. Try to start up from macOS Recovery and use Disk Utility to repair your startup disk. For details, see How to repair a Mac disk with Disk Utility.

• • If Disk Utility finds no errors, reinstall macOS.
  • If Disk Utility finds errors and repairs them, restart your Mac. If the issue returns after restarting, reinstall macOS.

1. If you can't start up from macOS Recovery or use Disk Utility, your Mac might not be turning on at all. In that case, follow the steps for if your Mac doesn't turn on.
2. If you're using an external display instead of a built-in display, make sure that the issue isn't with your external display. 

If the issue continues or you need help with any of these instructions, contact Apple Support. 

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

Sounds like a catastrophic GPU failure. That will require a hands-on evaluation by Apple.

Note the last line of your referring article: If the issue continues or you need help with any of these instructions, contact Apple Support.