serial mouse will not work

Hi,
I have an old pc with socket 3 cpu socket running win98. The pc will not recognize the serial. The pc has 2 onboard serial ports. 1 9 pin 1 25 pin. I have tried all settings in bios and still will not work. I tried new 9 pin serial cable and still not working. I added PCI serial card and no luck. No conflicts in Device Manager.