So yesterday i went to start my car in the -20 degree weather not expecting really that it would start because of the temp. so i turned the key it cranked slow and then i just got a sort of hum sound like the starter was just spinning and not turning over the car. i let go of the key and tried again and got the spinning sound. i thought w/e its cold i'll just start it when it warms up. I go outside like 15 min ago because its much warmer outside (a temp that it would usually start no problem) and i get just the spinning sound! no cranking just, what i think it sounds to be, the spin of the starter. Can someone help me out/tell me whats up? What do i do?