Is the mouse attached to the system via USB or PS2?
If you open device manager, do you see a mouse listed in there with an error
code next to it. If so, what is the error code?
Can you please clarify how you upgraded from XP Home to XP Pro ? What
service packs do you have installed?
Lastly, have you tried uninstalling the Intellitype mouse software and
reinstalling it, just incase?