XPS 15 9560 Screen with coloured pixels

Hello,

I've been having a problem in these last days with my XPS 15 9560. Suddenly coloured pixels show up on the screen and I can't understand anymore what I have on the desktop. Any image or text disappears and is replaced by random coloured pixels.

I first thought that was related to the internet connection since this started happening while using the browser, but it's now happening also with other applications. If in some way I move the windows or change from one app to the other it fixes itself, but sometimes just for a few seconds.

If I were allowed to attach some images I would show some screenshots. Did this ever happen to anyone? Any idea on how to fix this? The Dell Support diagnostic says everything is fine with the PC.

Thanks in advance,

Marco