If it fails to make the "NEW HARDWARE FOUND" noise under windows.
OR
Does not show up in device manager in windows either as a COM port or other device that needs attention.
AND
You have tried multiple USB cables that are DATA and POWER (they are not all the same).
AND
You have ruled out USB 3.0 issues by using USB 2.0
OR
You have tried it on other computers to see if they can see it.
Then I am not sure what else there is to try.