1.Try the device in another computer to verify it works
2.Check under device manager to ensure that your USB host controller is not disabled or with an explaination mark
3.Run diskmgmt.msc and see if the device is listed (while it connected)
4. If above is lited, assign a drive letter
5. If above is not listed, try a different USB port
6. Rinse and repeat
Another possible cause of this symptom sometimes can be resolved simply by removing the USB device, power off - rebooting, then plugging the USB back in, forcing an auto-redetect.