Since my original post I exchanged the board for a new one but the new one has exactly the same problem.
The following is a list, taken from an email I just sent to ASRock, of everything I have done and observed .
-The problem applies to both the two rear panel USB 3.0 ports and the two USB 3.0 ports fed from the header on the motherboard.
-If I disable the "USB 3.0 Controller" in the bios all the USB 3.0 ports work perfectly as USB 2.0 ports. As soon as I enable the "USB 3.0 Controller" there is no response from any of the ports (they still have power on them because the light on a USB 3.0 memory device blinks for an instant when I plug it in).
-I installed the drivers both from the ASRock download site and from the disk that came with the board.
-The Device Manager indicates that the "Intel(R) USB 3.0 eXtensible Host Controller" is properly installed.
-This is not likely a motherboard hardware issue because I am using a new replacement board with exactly the same problem as the original board.
-I did a clean install of Windows 7 Professional 64 bit on a new 256 Gb Samsung 840 Pro SSD immediately after installing the board.
-The problem exists both with the bios that came with the board (P1.40) and the latest bios (P1.70).
-The machine works very well in all other respects.
This is my first ASRock product and I am out of patience with it. I replaced my old motherboard mostly because I need the faster 3.0 ports and these ports will not work. Unless I find a solution to this problem I will simply consider the $85 cost a loss and replace it with an ASUS product as their boards have served me well over the years. I actually chose the ASRock board because it was a lot less expensive than the closest equivalent ASUS board but, unfortunately, this appears to have been a mistake.
(this is a different machine than the one in my signature below)
In any case, thank you for your suggestion.
