Alright guys I need help, I have a 03 6.0 and it was running perfectly fine until it got cold, now when I go to start it, it sounds like my starter gear it just spinning, I tried to tap it a few time with a rubber mallet just in case it was frozen, but still a no go I just put a heater under the starter to see if it helps, any ideas guys?

 

charge batteries, check all battery connections, check connections at starter and grounds.