Dodge Durango

My 2001 Dodge Durango won't start. It won't even turn over. I mean, when you put the key in the ignition, it won't turn at all. It seems as if its locked up or something but the steering wheel is not locked. Now, prior to this happening, when making sharp turns to the left or right, the truck wouldn't roll. I would have to press the gas to make a turn when pulling into parking spaces. But aside from that, it was fine and now the ignition won't turn at all. The battery is fine because the lights come on but you can't even turn the ignition to where the radio comes on or where you can roll down the windows. It doesn't turn at all. Can you please tell me why? :