UPVC Door Stuck... Help!!!!!!!!!!?

Hi, My UPVC front door won't open. The door is unlocked and the handle moves up and down freely (all the way up and all the way down). I believe the problem lies with the catch (the bit that goes in when you press the handle down and comes out again when you release the handle). This is held in by a screw, which has come loose in the past. How can I get the door open if the catch has become unscrewed/ the screw has come out while the door is closed?
Thanks
Cindy