What is the problem with the key? Can you turn it in the lock and the ignition or is it getting stuck.
If this is the case it's either the key or the switch. Are the keys you have from the manufacturer or did you have them made somewhere else?
If it's a new key that you need then you can call the Mazda dealership parts department and ask them what they charge to cut a new one.
If the keys work in the other door fine, then I would have someone look at the lock and the ignition switch to see if there's a problem.
〉 Answered on Apr 30th, 2007 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines