What is the exact model of the computer? You can get this information by entering your serial number here:
https://checkcoverage.apple.com/
Also what version of macOS is on this computer?
Can you see the login screen or do you have just a blank white screen?
Try booting into Safe Mode and running the Apple Hardware Test or Apple Diagnostics depending on the age of the computer.
You can try booting into Recovery Mode using Command + R to see if you can run Disk Utility First Aid or possibly to reinstall macOS over top of itself.
As long as the hard drive is healthy and you don't erase the hard drive, and the drive is not encrypted (Filevault), then it should still be possible to access the data on the laptop if you have access to another Mac or an external macOS boot drive compatible with this computer.
To create a bootable macOS USB installer you need access to another Mac.
You should always have good verified working backups of your system and your data. Make sure to do so from now on if you value your data.