Black screen on power up

I turned on my computer the other day and the screen wouldn't power up. I can hear the fan running and it makes the noise like it is turning on but nothing on the screen. I plugged it into an external monitor and the screen displays on it. If I shine a light into the laptop screen I can faintly see the images. My tech guy said it was the motherboard and would cost $600 to replace it. Before I go and buy a new computer or pay for the new motherboard, could it be something else?