COM Port Problems

I've bought the dell optiplex GX745, point of sale, w/restaurant solutions, and I'm trying to connect the Logic Controls customer display. I've followed the instructions about installing the drivers, however, I keep getting the same error message. CRE2004: System Application Exception: COM port not defined, use port property to set it before invoking InitPort. Also, this device is plugged into the USB port. I'm not sure how to define these COM ports. Please help.