Are you using Galileo's serial cable?
If you don't use the appropriate cable to connect to the Galileo's FTDI port you won't be able to connect to your board's terminal.
If you are using the appropriate cable maybe there is already a device called USB0 on your PC and your Galileo might be being detected with another name. To determine this you can take two screenshots of the output of the command ls /dev/ | grep USB, one with the board disconnected and one with the board connected.
Thanku Peter ! It was of much help. I will update you soon .