If ;)

the laptop is still under warranty, send it back and ask them to fix it. Otherwise,

1. check the function hot keys, sometimes, it's set to use vga output for presentation.
2. use an external monitor to make sure the system is working and the video card is ok.
3. watch closely on the LCD. if you can see some very dim images (start button, my computer, ...), your LCD is good. You need to replace backlights/inverter. Otherwise, consider replacing the LCD now.