Samsung R540 doesn't boot.

Hi,

I have Samsung R540 laptop and i don't why it doesn't boot. I can see power on button is ON and fan is running but they screen is completely black. however last week it booted once but then again it never boot as I already have mention that I can hear fan running. I have used some tricks like take out the battery and hold on power button etc, also I have tried chancing RAM but doesn't seems working any of that.

please suggest what cause the problem. do you think motherboard went faulty?

Thanks