The latch mechanism has an arm on it that contacts the door handle and when pulled, the handle pushes the arm and releases the latch. What's probably happened is that the arm has gotten bent and that's not allowing the handle to fully make contact. Remove the exterior handle, there's one screw that's probably behind the door gasket, and try tripping the latch using a socket extention...you can also just reach in with a finger to trip it. If that works, then the latch needs adjusted...probably by just bending the latch arm up towards the handle opening. Be careful as to how far you bend it, too much and the latch will trip with the slightest pressure...and you don't want that!
