If this has been answered already it may still be of help to someone else.
However, ignitions tend to wear out over time. Either a spring or a part inside them breaks, misaligns or just plain fails. In that case a new part is required, and will need to be fitted. That is the only option, although a quick solution is to put the key in but do not rotate it, give it a sharp whack with the base of your hand. Then try and turn it. Some times this moves things enough to get the key working. It is a stop gap solution only.