|There are numerous reasons why there is no picture on the screen. If there is "life" coming from the laptop (HD activity, login sounds...ect) then it is likely to be either a loose screen connection or broken video card/screen. A way to check this is to plug a monitor into the VGA port on the laptop and see if there is any output.|
If there is no life from the laptop (as in the laptop turns on but does nothing) then it could be anything, from the motherboard, CPU, RAM, GPU anything really that could have failed and is stopping the rest from booting.
Unfortunatly as laptops get older they are prone to just "dying" and not turning on. Make sure that the air vents are clear from dust!