I cannot turn the key in the ignition

Make sure the shifter is ALL THE WAY in the park position. A sensor must be activated to assure the vehicle is in park or neutral before the car can be started. Normally if you can't even turn the key to the accessories position, you should hold the steering wheel all the way to the right as hard as you can while trying to move the key and then if that doesn't work hold the steering wheel all the way to the left as hard as you can while trying to move the key. If none of that works you are going to have to get a mechanic to take a look. Also make sure you have the right key and make sure the key looks like it is not "bent" or damaged.