OK. First, have you tried the mouse in any of the other USB ports?
If this doesn't help, then go back to device manager & for each of the USB Root Hub entries :
right click, select properties->power management
deselect the 'Allow computer to turn off this device to save power' checkbox.
If that still doesn't help, you can download an SIS registry patch from this link :http://www.usbman.co.....nd Tricks.htm
Scroll down the page until you get to the 'SIS USB Registry Patch (Windows XP) heading & download usbdetect.exe.
There are also instructions there for refreshing the USB stack if necessary.
I recommend you create a system restore point just prior to installing the patch, just to be on the safe side.
Let me know how you get on