I have experienced same issue, and i have resolved.
I have win7 PC and USB3.0 card slot. installed firmware for this, but external HDD was not recognized as USB3.0.
what i have noticed is "power capability of USB3.0 card adapter". usb3.0 requires much more power than 2.0, and my USB3.0 card did not have 900mA capacity.
so what i did is buy "USB 3.0 A Male to Micro USB 3 Y cable for Mobile HDD" at ebay.
connect HDD to PC with both usb3.0 port and 2.0 (for power supply) port, then HDD works fine with usb3.0 speed!
you may need to check your usb3.0 card adapter can supply 900mA.
hope this can help.