My Ender-3 had been printing fine until the Z screw fell out of position and the Z stop fell off.  I reinstalled the parts but now the printer won’t auto-home.  When I initiate a print, the X and Y positions auto-home to 0 but the Z position first displays -75 then -3.99 and then everything stops.  When movement first initiates along Z, the extruder moves momentarily below the bed (at which point the display indicates -75), then repositions above the bed (but displays -3.99) and fails. The extruder remains positioned just above the bed at what appears to be the normal auto-home position but the print cannot proceed and I have to shut down the printer to reboot.