Try shining a torch at an angle close to the screen (when it is black) to see if you can detect a display at all. It will be dim, so a darkened room will help.
If you can 'see' a display then you have a problem with the backlighting. This could be a video cable problem, a backlight power supply problem or even a lid switch problem. The lid switch controls the backlighting either through software control or a direct power connection through the switch itself, I'm not sure which in regard to your particular model
If you can't see a display connect an external monitor to view its' display.
If it stays OK when the laptop's screen turns black you either have a faulty video cable, faulty or loose video cable connections at either end, (motherboard or screen), or a faulty screen.
If it also loses its' display, you either have a faulty GPU or a motherboard problem (which is probably the same thing as the GPU is most probably mounted onto the motherboard).
You could also try running the laptop in 'safe mode' in case it is a graphics driver problem. In 'safe mode' Windows only loads the basic drivers.