Do you have any unrecognized devices or unknown USB devices in the Device Manager?
You likely need to install the proper driver since you don't have the serial/USB adapters listed. I can't remember if I had to do that but I seem to think that I did for my FTDI adapters.
The adapter should have come with either a cd (perhaps mini-cd) or a manual/sheet/card that lists the proper URL from which to download the driver.