First of all: What do you want to achieve?
The Galileo isn't an USB device like a printer or a keyboard. It's a computer and the USB connection is used to communicate between the Galileo and your big computer. So it is normal, that the Galileo will not be shown in the device manager. The USB connection itself should present as a serial connection in the device manager. See the Galileo Getting Started - Windows documentation, especially Step 2, for further steps.
