Haven't used the car for a while so got the obvious flat battery.
Did the secret thingy to get in and now the door mechanism is playing up. Driving along and the door keeps popping open which is a bit a pain as you can imagine.
Would guess the solenoid needs adjusting - in behind the B pillar. Or it has got lazy, which can happen. The only other thing I can think of is the door lock has moved and is not hitting the striker plate properly.
How all this is related to a flat battery, I'm not sure!
The handle in the fuse box, push it in so as it has returned to it's resting position. Could be as others have said, but as you have moved it (handle) check this first, oh and charge the battery.