There are various faults that can cause this, hardware, corrupt bios, bad connections, bad solder joints on the mobo and a dead mobo.
So, remove your HDD and start your laptop. If its a dead HDD this should happen:
Power on – Fan starts – HD light on – POST screen appears – HD lights goes out and black screen appears with message "Operating System Not Found" and remains at this screen.
This is the first and easiest hardware fault to diagnose.