just downloaded V4.

I first noticed the window pane font seems missing, see attached. after this when i open a file i am presented with the open dialogue box, this works fine but after i have selected open I just get a big white box where the open dialogue box was. I dont see the desktop or other software in this "box"

I am on a iMac with system el capitan i think. I say i think as the proverbial white box won't let the about this mac show up!