Mice can start acting erratic for a number of reasons. First, we will try the easiest solutions. Often the "Male" mouse ball or roller is dirty, this means opening the trap door and cleaning. The roller normally only requires a fingernail to scratch off any accumulation of skin, dust and body oils. The mouse ball can be cleaned by removing the ball and cleaning with water or very mild soapy water. If the above does not fix the problem, or if this is a female mouse, the problem is normally a break or short in the tail. For those who are adventurous, or can't afford to replace, now is the time to break out the multimeter. With the multimeter, you will be needing to test continuity of the tail. Be patient, as you will often need to dismantle the mouse and disconnect the tail from the circuit board (or not depending on age). Often this is most challenging because the colour codes don't reflect any specific pin locations. Record the pin numbers and colour codes for later. At this point if it's only 1 broken wire, with an assistant ask them to slowly start flexing the wire in 1 to 2" lengths, when you suddenly have continuity you've found the damaged section. In the best case you will simply be shortening the tail length to bypass this point, otherwise you will need to wire up a new tail to completly replace the old one. If you find that no wires are broken, you will most likely need to replace. As the problem in that case relates to a damaged circuit board or chip. To return <-- Article by Slam, Last Updated June 2004