I have no experience with a Melzi board, so I can’t help if that is the problem. In marlin there is a safe extrude setting that prevents the extruder from working before it gets up to temp. Maybe you changed that setting some how to work on all axis? Try without end stops as well, people tend to use them wrong initially. I have had several people having issues because of their end stops. I don’t recommend them they can be a hindrance in milling. You can plug them back in after it is working. Maybe there is a setting in repetier but it is not on by default. So maybe uninstall and reinstall.