Thanks for all your responding !!
Still i don't know, why the Dell people are hiding from this issue? I hope at least the forum moderator should respond to this issue as several their customers are suffering with this problem. Waiting for help.
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,
I too installed an oem version of Windows 8.1 on my Dell XPS 15Z laptop and have the same problems your are
having with the screen. I installed dells Windows 8 drivers but I still have the same problem. I think Dell wants us
to buy their new updated Dell XPS 15 (9530) laptop which cost close to $2,000.00 dollars. Windows 8.1 is way
faster than Windows 7 so I'm going to keep it and hope one day Dell will find it in their hearts to develop the
drivers for the Dell XPS 15Z Windows 8.1 install.
I noticed that I have this exact issue when I install Intel HD Graphics driver from Intel.
But even with Dell drivers, I constantly get slight flickering on the top of the screen while on battery, flickering in the Welcome screen, flickering while watching videos on Potplayer whether I'm on battery or on AC. And on top of that, very slow screen launch after Windows loads up.
This issue made me roll back to WIndows 7
I started getting the weird screen about 2 weeks after i got Windows 8.1 Pro. The thing is that it messes up a lot only when a window goes full screen or if it touches the border of the screen.
Lower your refresh rate. When I installed Windows 8.1 OEM version on my Dell XPS 15z laptop I was getting a fuzzy screen. Like the screen was malfunctioning. I was about to revert back to Windows 7 when I lower my refresh rate from 60 to 40 and it WORKED. You don't know how happy I was.
So Bhakti try that and see what happens.