Black screen upon startup

When I turn on my notebook, the screen stays black. At first it only happened a few times, and was remedied when I restarted the computer. But now, restarting it is'nt working. I know the computer is working fine, those few times I restarted the computer it was working fine. I did'nt have any devices or USB's connected to the computer, so I know it's not a device causing it. I'm at a loss for what to try. Anyone have any suggestions?

Thanks,
Alexandra