Salesforce support are the only people that can help you. Usually they make you jump through some hoops for "security reasons" but this isn't uniformly enforced. Some will even tell you they can't do anything for you, so it takes some effort. The moral of the story is to never mess with a feature that can irrevocably lock you out unless you're willing to risk losing the account. Only paid customers can get their account fixed, while developers are usually told they are out of luck, unless it is an ISV developer org that they need for their business. Non-paying users are ignored, and have historically always been so.