Switch on laptop(studio 1555) but black screen

when i switch on my laptop (dell studio 1555), nothing on screen, can't enter bios (fan running and dvd rom have function), why???

need switch on and switch off so many time, sometime lucky then can enter bios and boot windows normally. Even i change bios setting boot from disk and clear cmos load default, the problem still happen.

is it my hard drive problem, lcd screen, motherboard or bios.......???

HELP..............