It probably rusted out of position and rusted the spring mechanism. Mine did this as well. I had to push up on the handle really hard to release the latch. You might need to put a towel on the bumper and pry the thing upwards with a long screwdriver or something. Then I hit it with some 3 in 1 household oil (like WD 40) and wiggled it a bunch until the springing mechanism came back to life. When you do get it open, you should be able to see down into where it latches. you'll have to push it back into a proper position before you oil it and close it again.
Sorry, it's tough to explain in words and I don't think there's any way to get you a decent picture.