Can you hear the fan or the hard drive spinning when you're trying to start your laptop? If you can, please try to connect your laptop to an external monitor to see will there be any video signal going out from the laptop. If you can see the desktop on the external monitor, but you cannot see anything on the display probably you'll have to make and LCD inverter replacement or at least changing the flex cable. If there's nothing showing either on external monitor nor display, but the fans are still working, the problem that you have may be due to the failure of the video chip. Sometimes, after much of a use and less cooling the graphics processor which is responsible for video signal transmission get unsolders, the thermic paste goes away and it gets unsoldered, therefore the screen doesn't show anything. If you know some stuff about the laptop's hardware you can change the thermic paste yourself by opening the laptop and checking if the chipset that is next to the processor has got unsoldered or you can bring your laptop to a technician to get it soldered again.