« Does the computer see the board over USB? »
The next thing we need to know, is whether the computer recognizes the Smoothieboard over USB.
Connect the USB cable to the Smoothieboard, and to the computer.
Your computer should notify you that a new peripheral was connected, and allow you to access the files on the Smoothieboard's SD card via your file browser.
If you can access the files, click on Yes.
Otherwise, click on No
By default, most Operating Systems will automatically mount the Smoothieboard ( ie. warn you that the Smoothieboard was connected, and offer to show you the files ).
However, if you disabled auto-mount ( you know if you did ), you will need to manually mount the Smoothieboard to check if it can be accessed.