You will need to do this with the key board if the mouse is not working.
Go into the control panel and click system and maintenance look for device manager and click on the update device drivers.
Go to mice and other pointing devices and select the offending mouse driver and either try updating it or removing it.
You could also try plugging in another mouse to see if it works first and then delete the drivers from the device manager.
I would also recommend that you check to see if the USb port is working. has your client tried plugging the mouse into a different USB port?