Some of the symptoms of a laptop with a bad LCD inverter.  You will experience some of the same symptoms if the backlight is bad as well.

1. System powers up with sond but no picture on the screen.

2. Screen is dark but you can see a very faint image on the LCD screen.

3. Screen flash for a second then turns black but the laptop is still on.

LCD with bad backlight inverter

LCD with bad backlight inverter

Boot up your laptop and flash a flashlight on the screen you should see a faint image.

Connect your laptop to an external monitor and see if you get a picture(You will need to use the function keys on your laptop to switch your display to the external monitor).  Your monitor should come on.  If not, then the issue is not related to the LCD inverter or the backlight.  In that case the video card on the systemboard is to blame.