URGENT Help needed with PNP on com port

I have a PABX system that runs on the serial port - com port (Win XP) which when plugged in is detected by PNP as a microsoft serial mouse. When detected it sends the mouse pointer crazy and I can't use the computer nor the pabx. It shows in the device manager as the microsoft serial mouse. I can unplug the pabx but it disappears from the device list so I can't disable it (even if that is the correct solution) as a mouse and when it's replugged in the pointer is too uncontrolable click on the device. If I start the computer then plug in the pabx on the com port it works fine but when rebooted with PABX plugged in the pointer goes crazy again. In this part of South Africa the electricity goes off sometimes for so long that the UPS dies. I despirately need a solution that is better than teach the operator to only plug the pabx in when the computer has booted.

Does anyone have a solution. Thanks, Jivan