Also this from the "ifixit" website:
"Mouse is on, but cursor is not moving
You’ve verified that the mouse is on (for optical mice, there is a light on the bottom), but moving your physical mouse doesn’t move the cursor on your screen.
Using wrong surface (mouse pad)
The mouse might be unresponsive because you have it on a clear or shiny surface. The mouse needs a surface that is able to reflect the outgoing beam from the LED back up to the sensor in the mouse. Textured surfaces are better, because they allow the mouse to recognize movement easier. Choose a mouse pad that is not shiny or transparent. You can temporarily use paper or a folder of some type to place underneath the mouse.
Mouse is dirty
If the bottom of the mouse is unclean, dirt can interfere with the sensor. Use a moist towel or wipe to clean off the bottom, so the light has a clear path back to the sensor.
Computer settings are wrong
Your mouse settings may be disarranged in some way. To fix this, go to your control panel (Start Menu or Windows Key -> Control Panel). Next, go to “Hardware and Sound” and look under “Devices and Printers” (note that “Devices and Printers” may be directly accessible from the computer’s Start Menu). Select the “Mouse” option. The settings will then pop up on your screen. Select “Default” and then exit out. This resets your mouse settings to the normal settings. If this does not work, then try restarting your computer. Unplug, then replug your mouse back into your computer after the restart process has finished"
message edited by phil22