Thank you mate, it actually made me understand better what you did
I am pretty sure it's a cable connection problem. I cut a small part of the cable, the keys are working again but not all of them... and when I unplug-plug the cable, another set of keys work and other set of keys stop working. I've managed to make all keys work at some point just by unplugging/plugging, but never all of them at the same time.