My laptop screen stays blank while it is on

when I switch my loptop on ( lenovo 3000 N100) it goes go and everything work well but the screen stays blank, I tried to open it and clean components inside thinking that the problem caused by dust or rust but still the same so what might be the cause? which component might be damaged? and I tried this thing of saying I have to remove chager and battery and press power button for about 2 minutes and 30 seconds and put back battery and start up and still screen is blank