If you are having problems with the screen door lock it might need to be lubricated or just replaced. Most screen handles do not work just because they might be to tight or to loose, so try to get a screw driver and tighten it properly and that will usually fix the problem.
We are a mobile screen company with 15 years experience in screen doors locks and we would be happy to give you a hand. We give estimates at no charge, just email me or a call.