Key won't turn

Hey guys I ran into a very weird problem. Parked truck last night and got into it tonight and battery was dead so I jumped the truck and get in and the key won't turn in the ignition! I am very mechanically inclined so right away turned the wheel and tried nothing so than played with the shifter and still nothing! The key doesn't show any copper on it so it's not wore down and it slides in the ignition smooth just won't let me turn it. Any ideas!?

Try auto start first