An IRQ or resource conflict could be an issue. You can check in device manager for this. If you have Win9x you can right click my computer and goto properties. You should see a tab for device manager. Check modem properties for a conflict. You canalso check under ports to see if there is a conflict listed there with your printer port. To get to device manager with Win2K or XP click manage instead of properties. A window should open with a listing for device manger. Check in same manner. Ifa conflict exists you can try manually setting the IRQ or conflicted resource. There should be a box that says USE AOTOMATIC SETTINGS. Uncheck this box and you should be able to make changes.
If the problem is not resource related you might trychecking BIOS settings. You might try changing from Bi-Directional to ECP, EPP or the like. Or whatever may be available.
If available you might try installing on another PC to see if it will work there. Might try reinstalling the drivers if you havent already if the previous suggestions dont work or dont apply.
Hope this helps or gets you in the right direction.
Jason