When you turn the key, a linkage pulls a pin out of a lock ring inside your steering column. For some reason, your wheels are forcing the steering column lock ring against the pin with enough tension that you cannot turn the key.
Solution: Look to see which way your wheels are turned. Turn your steering wheel the same direction (away from center), and turn the key at the same time. It may be fairly difficult to do, but unless something in your lock ring is physically broken/jammed (which is VERY unlikely), this is what needs to be done.
Good luck.
