I have seen the responses of many regarding the F8 to try to fix. I will try this later today, but my question is when this happens and you shine light on the screen you can see that it is on. Is this a different situation than the others?
If you can see the image when you shine a light on the screen. It means you have a problem with the "backlight" or the "inverter" that powers the backlight. Either of these problems requires you take the laptop to a qualified repair shop.