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The problem is the latch mechanism is stuck in the "in" position. You will need to either removed the panel from the inside (hard to do) or attempt to move the mechanism with a long screwdriver or slim jim back to the "neutral' position so you can open the door. Each time you push the outside door button, you are pushing the latch mechanism 'in'. That is what you have to return manually. Once returned, you can unlock it and then open the door, but it will stick 'in' again. After the door is open, you can lubricate and work the latch so it returns freely on its own.
You need to look inside the door between the glass and the inside of the door shell. Try and see where the outside handle linkage comes in contact with the latch. a flashlight & good eyes from the right angel are required.
Once you see it, you will understand and be able to see that it is not returning by itself and you will have to help it by prying the mechanism back with the screwdriver. The screwdriver will probably need to b at least 18" long to do the job. If you can't see it or get to it, or if it's covered by window channels, you will need to remove the inside door trim panel with the door closed.
Here is a picture of a complete lock/latch mechanism.
The part with the arrow is the part you need to find and push back. Every time you open the door you are pushing the latch in the direction of the arrow and it releases the mechanisms within the latch. If it sticks, you cannot lock or unlock, or open the door until it returns to the neutral position.