You said in Post #4 that it showed the calibration screen. The way that screen is reached is by putting the nuvi into preboot by holding the screen and powering it on, a healthy nuvi x0 device will go into preboot for 30 seconds them move to the white screen. It you connect it to a PC by USB holding the screen, it will won't move into Mass Storage Mode, after 30 seconds going to calibration and staying there if you don't calibrate the screen manually. If you do it will boot normally even though it's connected to the PC (a handy trick to charge it and operate it normally).

You can see easily if in fact it is or isn't in preboot by holding the screen and connecting to PC. Have Windows Device Manager open and visible on your desktop first and watch it's GI, when you hold the screen with the device fully OFF and plug in the USB you should see it show in Device Manager for ~30 seconds then it will try to go to MSM as the green line appears on it's screen if you stop holding the screen before it moves to calibration.

[Only registered and activated users can see links. ]

When in MSM a healthy device will show as 'Garmin nuvi Flash USB Device' in Disk Drives and 'Garmin Devices' will have disappeared from the principal list. As your nuvi cannot reach MSM it defaults to boot normally instead.

Better to make absolutely sure that it cannot enter preboot using either the hidden menu or holding the screen by experimenting as I've detailed above before trying to do anything with sd card text commands.