Try shining a torch at an angle close to the laptop's screen and check for images. They will be very faint if they are there so trying in a darkened room may help to see them.
If you can see them, try connecting an external monitor (TV?) to the laptop's HDMI port and check it it shows a display when the laptop is on
Press Fn + F5 (both together) to toggle the display between the laptop and the external monitor.
If there is a display on the monitor and you can see images then there is a backlight problem with the display. Either in the screen, the video cable between the motherboard and the screen or the motherboard.
If you can't see images and there is no display on the external monitor then there is a GPU or motherboard problem.
In either case the laptop would have to be opened and further testing required to find out what's wrong.