I've experienced this problem twice before. The first was solved by pressing Fn-F8 or whichever buttons on your keyboard change the display mode (should have a picture of a computer screen or say something like "LCD/CRT"). As it turns out, my 1-year old nephew had been bashing the keys and had disabled the LCD portion of it by a stroke of bad luck.
The second was more closely related to your problem, with the display unreadable unless a flashlight is focused over it. The problem is likely the inverter, which can be easily and fairly cheaply ($50) replaced. However, as was the case for my old laptop, there's chance that the LCD bulb has burned out. Though bulbs are cheap, bulb replacement without damaging the screen is difficult at best and impossible at worst for many laptops. Unfortunately, the only way to troubleshoot is to invest in the inverter (system specific) and hope that it fixes the problem.
Good luck!