Why would the file system (CIRCUITPY) of an Adafruit board running CircuitPython not show up when connecting it to a suitable host via a micro usb cable?
Besides your first answer about the cable, because of the relatively inexpensive nature of the boards and direct access to their power/ground sometimes the EPROMs that the file system are hosted on just go bad and give unexpected results. Best idea is to:

Test your environment with another board.
Reflash micro python on your board so you can start from scratch (didn't mention if you'd tried that).
Why might an Adafruit CircuitPython board's filesystem fail to mount?