Optical mice use a motion sensitive LED to track the movement of the mouse rather than a ball like old-fashioned mechanical mice. Disassembling a Microsoft optical mouse is a good way to see how a mouse is put together. It's also good to know how to do this if you ever want to give your mouse a thorough cleaning or replace the LED light. Disassembling a Microsoft optical mouse is perfectly safe and shouldn't do any damage to your mouse.
Unplug the mouse from your computer.
Turn the mouse over. Remove the two black pads near the bottom and take out the screws with the Phillips screwdriver.
Wedge the flathead screwdriver between the top and bottom of the casing. Work your way around the mouse, beginning on one side of the wire entry until you make a full circle. Gently pry open the casing as you work your way around the mouse.
Slowly pull apart the top and bottom pieces of the case.
Remove the screws holding the circuit board in place and carefully lift it out. Gently squeeze the LED with your fingers and pull it out of its socket, which is attached to the circuit board.
Use a high intensity LED if you replace the light. The brighter the bulb, the better the responsiveness will be.