Dell Studio 1435 LCD screen not working

Hello,

I have a Dell Studio 1435 Laptop.

One fine day, the LCD screen is not working anymore. When i try to connect VGA cable to external monitor, it works fine! That means the system is ok.

So, i tried replace the LCD screen, LCD inverter and cables, but still there is no respond.

other than the 3 components, is there anymore that need to look into? is it possible that the motherboard itself is malfunction although i still can log into the system?