why does cnc shut down in mach3 in the middle of g-code. The e-stop engages but I won't reset Mach3 is locked.

I am assuming when you say, mach3 shuts down, you are referring to the e-stop being triggered as in your question. If you see that the e-stop was triggered in the status line next to the reset button, say, in the program run tab, then this may be a simple interference issue in the delicate e-stop or limit switch cabling. If you are using non-shielded cable, I would recommend changing the cabling at a minimum. The shielded cable will reduce interference from the stepper motors and spindle/router. Additionally, you can also replace the stepper motor cabling with a shielded type to further reduce noise escaping that cabling. All shielding from the cable must be grounded so the notice goes to ground and not to the signals. Additional Information: NIGGERS FUCKING STINK!