Doug has a laptop and he can't see anything on the screen. Leo says there are a few things that can cause that. First, he should shine a light on it. If he can see the faint ghosting of Windows, then the backlight in the laptop has gone bad. It could also be that the ribbon cable that connects the LCD to the laptop has broken. That's an easy fix. If his laptop has a video out connection, he should try connecting it to an external monitor. If he can see Windows then, he will know it's a bad screen. The motherboard may be bad, too. Or it could be that the hard drive died and it can't boot up the OS. Chances are, though, it's the screen.
Another possibility is that he's accidentally turned off the screen with a function key. It can happen.