OK, I'm a bit behind times, but I've just bought my first USB3 device, a Segate 4TB external drive.
When I plug it into a USB2 port it is recognized and could be used, so it'is OK and its cable is OK.
When I plug it into either of the USB3 ports nothing happens.
Similarly when I plug a known good USB2 memory stick into one of these ports there is no response other than the led on the stick lights - so it's getting power.
There are one or two other posts on this site about this problem but none of them seem to cover my symptoms exactly.
Any ideas?
I found some newer USB3 drivers on the Gigabyte site and they seem to have done the trick.
Panic over.