most likely the backlighting is gone. If it's in a docking station or thinks it is, it might've turned off the internal monitor though. Check with fn+f4 (or whatever the screen shotcut is on your system) or attach an external monitor. Also check that the small plastic thing that tells the system that the lid is closed isn't stuck.
If the backlighting is gone, the laptop will be too expensive to repair. use it as desktop replacement or discard it.