The cylinder lock for the ignition switch may have a problem. It has a lock which does not allow it to be turned without the key and a lock to keep the key in once it is in the, "ON" position.
If the key is a sopy, that may be your problem. Take it to the place where you had is made and have them clean up the key.
Otherwise the ignition lock needs to be replaced. You may try jiggling the steering wheel back and forth to see if that helps.