RE: My DELL XPS 15Z screen issue.
The 15z has a hardware problem as I have since discovered.
Tried win8, win7, various drivers and OS settings.
The screen distortion tends to kick in with USB activity. It can be stopped for a short while by gently twisting the framework of the keyboard/case assembly. So I think a cable, or solder joint has let loose.
I have had it apart several times checking various components and cable connections, but can find nothing so far.
It may be something to do with the power supply - when it is likely to go in and out of the distortion mode, I see various low level variations in backlight intensity seemingly moving up and down the screen. When its working ok, the backlight is steady.
Bummer, it is (was) a nice machine,