I recommend you study the laptops behavior as it boots up (if it boots up). If it still seems to run normally aside from the screen being black then the problem is quite obvious. Find a monitor and plug it in and repeat the process of booting it up. Note some laptops may not hand over the display output all the time. Try closing your laptop or perhaps using different input plug. If the monitor works, you may try resetting everything including your os.

If all else fails just take it to a computer repair shop to have a technician analyze it properly and determine the issue. As I said before it can be a number of different issues and computers aren't always straightforward. If the laptop is well and truly outlived its life and you need to retrieve your important files from it, then retrieving the storage drive is pretty straightforward with most laptops. Just pop the bottom panels off and you should be able to see it along with the ram (which can be salvaged for later use if its any meaningful size). After that just plug your storage drive into another laptop or if you don't have the means then bring it to a computer shop.

hope your laptop isn't completely dead though and it won't come to that.

Good Luck :)