Communication Port Not finding card reader

Dimension XpsT with Windows98 system. I had been successfully using a brother memory card reader connected through serial port. Now when I try to use it I am receiving a message saying that the card reader is not connected, I have powered off, checked the pins and reconnected. The in-service light on the card reader is activated when trying to access the reader, but the system is still telling me that the reader is not connected. The card reader is working when connected to another computer. Where/what should I look/do from here? Thanks for any help.