Ron,
Nothing happens when you move the handle up and down. The owner had a thing about doors. You could only get in through the front door with a key. All other doors have no key access. Do you think this has anything to do with this?
If this is an Andersen French patio hinged door with 2 operating doors, this is the way you open them. I have one in my house.
Take a picture of the door and lock.
When you push the handle down, you need to put a good deal of pressure on the handle.
How do you lock the operating(active door)? It has 2 bars on the doors edge that locks into the stationary sash. You must lift the handle up so the bars extend outward into the other door.
Possibilities:
The previous owner modified the door so the lock can't disengage.
The door is not an operating door and the handle is just for show.
-If both doors have hinges, they both should open.
Operator error.