Diagnostic step:

* Remove the system ram and press power on to see if any beep sound come out. If it beeps then it can mean the system board is working.

1. Unplug/detach  the video cable form system board.
2. Laptop connect to an external monitor, then power on.
3. Hit enter BIOS key. <= tested with Acer.

Scenairo 1: No display on the external monitor, means the system board is defected.

Scenairo 2: External monitor has display (entered BIOS), could be defected monitor or the cable. Order testing part first.