The problem is likely with the parallel port card.
See if there are any settings in the driver that came with the card that can be adjusted. Many of these cards are designed for printers only.
A second possibility is the serial cable you are using. Check it with a meter to confirm that it's straight through and that all 25 pins connect, a modem cable will not work properly.
If you can, try another computer with a built in port to confirm that the machine and cable setup works properly.