My anti theft AND door ajar light on the dash

In my 2006 ford escape sometimes it won't start. I'll turn the key over and have power but won't start. It has no crank. I've noticed that the anti theft light flashes. I've read in owners manual and it says that mean there could be a problem. I've read all these different articles on how to deactivate it and have tried them with no luck of any of them fixing it. It dawned on me that everything I read started with “make sure all the doors are closed" as i see with my 2 eyes yes they all are closed….. but the car thinks one is open. On my dash the door open light is on. I have narrowed it down figured out that my light gate is the door the car thinks is open. And thats where I'm stuck! How do I get the door ajar on my dash to go off so I can fix the anti theft????