uPVC doors can be very temperature dependant. Fixing a dropped one can be as simple as turning the screws (though it sounds like you've tried that already) right up to as hard as stripping the door down and re-building it from the frame up.
The procedure most likely required is called a "toe and heel". Any good locksmith who knows his uPVC should be able to assist.
Discreet Security Solutions, April 2009
