Goffroy,

you did some work on the spindle if I remember from your other thread. You sure that the grounding is still intact in there?

Also I cannot tell from your photos if the shield of your stepper motor cables is grounded. Each of the sockets in the control box should have a solder tang to allow them to be grounded too unless they are designed to be used with a metallic box.

Finally, is your actual house wiring set up correctly with a good ground to real ground?