As far as I remember the G920 cannot be switched to XBox mode, nor does it need to be. When the G920 powers up, it sets itself to the XBox mode by default. If it's connected to a PC, the driver then picks up the device's ID and switches it to PC mode with a magic packet.
From your post it is not entirely clear what is happening. XBox is not really good for diagnosing this though. Does the G920 show up at all if you plug it into a PC? If it's not even listed in the Device manager, you may be looking at a faulty HW. You shouldn’t be looking for the G920 in the default mode amongst HID devices because the XBox mode doesn't work as a HID device.