1) First of all we are going to create the front side of the monitor (desktop). Make 4:3 ratio like this below:

2) Convert object to editable mesh and select all the outside edges. Hold shift and drag  them just a little bit to the front.

3) Now select all polygons of “desktop”, go down to Edit Geometry and detach them.

4) We are now done with “desktop”. Again select outside edges, drag them to front and scale them a little. You should get something like this.

5) Select one by one side edges and drag them as shown below.

6) Picture below says everything: drag and weld, Do this with the rest of the 3 corners.

7) Drag the outside edges back a couple of times.

8) Select one of the sides of mesh and delete it.

9) With selected object go to mirror and check x axis and instance.