Computer Mouse Problem

Help! Is my computer mouse sick or just lazy? Often I point and click, point and click and nothing happens. Eventually it works. This morning I gave it a good shake in frustration and that seemed to do the trick. I have taken it apart to make sure it is not full of dust bunnies, but it is fine. I have a Dell computer system that is only three years old. What is the life span of a mouse anyway? Thanks for any knowledge you can give me.