I don't know how to get the stem off, after taking the handle off and the plate off, there is another piece that has a little screw to right,does that somehow com off and if yes how ?

I believe Harden is a model name for a brand made by Symmons. This should be your spindle or stem Symmons/Harden TA-10H Spindle - Locke Plumbing Once the packing nut is removed have you tried turning the stem counterclockwise?