There are several ways, you can press F-8 right before auto-exec takes effect and follow the prompts using common sense and tell it not to start cnc. If it is already powered up, go to "PARAM" , "SETUP", type "PROTO3", press enter, level 3, enter again, then a DOS key will become active. At this point you can either press the DOS key and exit the CNC into DOS, or escape out to the main menu and go to "DISPLAY" and enter the SHELL, if you enter the shell you can return to the cnc by typing exit at any point. Just remember, most changes won't take effect until a power cycle or at least running auto-exec again.