It appears the the latch is now out of adjustment or broken.
To check this you would have to attempt to remove the door panel. You should be able to get to the linkage to door latch and work with it until the door will open.
By now you should have found the problem and do the required fix.
May, 22, 2013 AT 8:51 AM
These latched are cable operated and the cable will stretch and therefore it takes more pull on the handle to open till it gets to a point where it won't open. Check that too.