Does the screen diagnostic (hold D through powerup) produce visible test images? If it does, you likely have a bad GPU. If not, there are two possibilities: a  bad screen, or a bad backlight power supply.  Since the latter means replacing the mainboard, start with the screen, which is the less expensive part.  The other option would be a reputable repair shop that can test the output of the backlight power supply, or test the screen on a different system.  
I'm having a similar screen problem, after Windows update, screen doesn't "work" any more? Is it a driver thing? If I do a screen capture of the Laptop screen with all the lines, and drag the "snipped" image to the other monitor, it shows the actual desktop screen that should be there? Sometimes after an hour or so the screen works till I turn it off?  [IMAGE]
17 R4, screen problem