I Have A 2009 Nissan Maxima and at first my car would not start but now my fob key will not work it's not the battery it's new i changed the battery in the fob key too..

 

Hey! Try checking to see if you're getting full contact on the battery terminals. Also, check your fuses to make sure they're all getting power. If you're seeing a yellow key on the dash then it could be your security system for the steering wheel lock. They're funky on the Maximas and can keep the car from turning on at all. It's recommended to remove the fuse to prevent the issue further down the line. Hopefully, you can get your Max running!