Penmode + shadows look COMPLETLY different on different computers

I got several computers. One usually shows a decent pen-view of all models to show for ideas. If I add shadows it adds a tint of depth, not too different from without shadow. But this computer which is the fastest (and I prefer to work with), penmode with shadows looks like total crap. It completly deforms the image. I open the display-options settings but I cannot figure out what causes these 2 computers to show such different results. Anyone can help me?

To illustrate, I made this model, pen mode is the version that looks ok, when I put on “shadow” as the only change it because worthless.

Hi Goran - does this happen with just a box or two in the scene? Can you please try resetting the Pen mode to defaults and then just add the shadows in - same problem?