HP laptop not booting

Hi,
Well.. I have this laptop named HP but I don't know the model number. I pressed down the power button with the power supply but the screen doesn't display anything except a black screen. I followed the instructions about pressing the power button without power supply for 1min and turn on again with the power supply. Unfortunately it doesn't work on my computer.. What should I do next?

I really need this computer to work for I have important stuffs saved in it.