I am not a CGminer user, But I just downloaded it to try it out, And that does not detect the FPGA either. I have checked it detects the other three and it does, As far as I can tell, Its something with the boards, I have checked everything else against all other components.
Is there a reset? What is used to flash these things? Is there something I can download to see if it can find the device?
You should see them in device manager as FTDI USB to Serial Port (com xx). It might be a good idea to wait the next version of cgminer which shouldn't require you to add any parameters.
Do you have any leds blinking when you plug it in and turn them on? If not, check the fuse (big white cube on the back of the board), it might have burned out due to a short circuit.
To re-flash them you need a JTAG cable. We have tested every one of them and we only shipped working devices.
However, if you are sure that they're defective send them back and we'll replace them for you.
Regards!