My screen is full black, no back light. Nothing.

When I was using my laptop in widows10, 64 bit, the display driver became not responding. Then there was some sort of error. The display was working. I reinstalled the windows. Now its windows7. But laptop's display is not working, but when connected to external display by RGB, it's working. But the laptop's display is not working, no backlight. I once changed the boot type in boot settings and the display cameback, but its not booting. I'm currently screwed.