Did you assemble the motor shield yourself?
How do you have your motor connected? Did you try any other connections?
What else are you touching when you touch pin3? Does simply applying pressure to it do the same trick or does it need to be your finger? Is the shield inserted properly?
What do you mean by "some pins on the processor"?
Maybe sharing the code might also be helpful.
Right now we have very little to go on in order to help you.