Now that its winter, when we try to start the.

Now that its winter, when we try to start the car early in the morning the motor won't do anything. All of the lights, radio, etc work fine but the motor won't so much as make a click or even try to turn over. If I wait a couple hours when the sun comes up and it warms up a few degrees it will start just fine. I checked the antifreeze and its good to -20. Its only been getting down to the mid 20's in the mornings here in Missouri. Any ideas on something that would be that temperamental?