This is usually caused by lack of power to the card. Many of the cards using our USB 3.0 host controllers have a power connector that needs to be connected to the system power supply.

If a power cable is not connected then the controller may show up in Windows Device manager but disappear when any USB devices are connected to the controller.

WHY???

In order to provide enough power to change phones/tablets/etc quickly on multiple ports the card needs more power than it can get from the system PCIe bus.  The extra power connection provides enough power to charge all those power hungry devices quickly.