@Fonfon I’m in the same case of you, my screen don’t turn off.
I was wondering if my PIR wasn’t broken but I wanted to check it before.

So before changing your PIR you can test it by a simple python script. I found this (in french) : http://mycoolpizza.blogspot.fr/2013/05/raspberry-pi-utiliser-un-capteur-de_29.html?m=1