What is wrong with my ignition,when I put the key in it won't turn ?

Tom, I have found the same. Also, it is possible to break the mechanism in the steering column by putting too much force on the key.
As Tom mentions, turning the steering wheel relieves the pressure on the mechanism and will help to prevent breaking it.

I have seen this on many vehicles. It is entirely possible that when you last parked and shut it off you had the steering wheel turned to the left or right rather than centered straight ahead. The power steering was assisting with holding it in that position until you shut it off. At that time power assist stopped and the wheel is resting firmly against the theft lock mechanism. Grasp the steering wheel firmly and if your front wheels are pointed to the left then force the steering wheel to the left a bit more and turn the key will holding the wheel, if front wheels are to the pointing to the right then force the steering wheel to the right and turn the key. Try NOT to turn off the ignition with the wheels not pointed straight.