Acer aspire 5050 lights up and cpu lights up

Hello,
My acer aspire 5050 lights up also the cpu lights up for about 2 minuts then all lights are gone. My screen remaind black. No light shows up. However I am confused regarding my problem is it mother board or the screen. I am not able to Identify which one is at fault. Also except for cpu light other caplock and numlock key donot light up when pressed . Hope this gives enough clue to identify the problem. Any advice thanks