Set Matte not masking layers the same I am trying to use a shape layer with set matte to mask off everything behind the screen, but it does not appear to be working here is a video 
                
            
Please help
Not sure about Set Matte, but you could try setting the transfer mode of the shape layer to Silhouette Alpha? That will cut out everything beneath that layer.

(You currently have the transfer modes hidden. Right click on the title bar above your layer names, click to Columns->Modes)