Have you checked that the connectors are connected correctly? There might be a typo in the manual. Google the pinout and make sure the D+ and D- connections are right. Maybe the internal cable was mislabelled. Try leaving the V+ and GND where they are, and swapping the D+ and D- connections (If it's the kind of cable with separate connectors). Failing that, just try replacing the internal cable that goes from the USB port to the motherboard..
It might even be the cable you're using from the computer to the device. Some are wired as charging cables only and don't even have the data wires. I have a few that I had to label because they can charge but can't actually connect any devices.