If the backlight goes out then you should still be able to see something on the screen, though it may be extremely dim. If you put the laptop under a direct light source can you make out faint images? If you see nothing, this may be a problem with the LCD itself or possibly with the video card. As noted, you should be able to get the key combination specific to your model from the manual, if not you can attach an external monitor and try all the FN+F* keys, though one of them should actually be labeled with two screens or LCD/Mon and that would be the one. At the very least, most models if you attach an external monitor will display the BIOS screen on both displays by default. If you get an external display to work, then it is likely not the video card, but the the LCD alone that is the problem. If you see anything on the LCD it may be the invertor and/or lamp of the backlight that is bad, and if you see nothing the LCD itself may be malfunctioning. Or it could just be a loose video cable from the motherboard to the LCD.