Can't see preview

[Julia5CF5]

Screenshot attached below-- I can't see my composition, the screen is completely black. I have no idea what button I pushed to make this happen, and don't understand enough about After Effects to know what to try. Does anyone know why this happened to me?

[ToolfarmJP]

You seem you place some footages on the timeline. Nothing is displayed when you move the slider on it? If so, I would recommend you update the graphic driver.