can you provide more details about the problem?
you installed a new usb controller card in your computer and it's not working?
or you got a new flash drive and you connecting it to the usb but new device is not showing up?
if it's the latter then check in device manager if device is detected at all (it should be listed as mass storage device or something of that type if it's automatically detected at all) if not it could be listed as unknown hardware.
how old is your computer? what model is it?