PLEASE HELP!!!

Hello, 

I am going crazy... Last week I must have hit a wrong button accidentily and now I can't see my composition anymore. I noticed that it says "Wireframe" in the corner but I can not find it anywhere. To illustrate my problem: when I press play for the preview of a video, it shows the video: I can see everything. But as soon as I pause the preview mode the screen goes black and I only see the layer controls. I have been searching possible sollutions for this problem for a week now but without any succes... Please, help me!