It's the electrical part of the ignition switch. I've had this problem before.
Which part of the ignition switch did you put in? On mine, one of the wires that was sodered on broke off. So, if you put a new electrical part of the ignition switch in and it's still not working, check the soder on it, as well.
Also, this topic has been covered in detail-that's how I was able to figure out what was wrong with the car. So, that being said, do a search for more info if you need it.
Okay, so I decided to not be lazy and get you the link...
Having probs with the lude.. let's see how can