How do I fix my upvc door?

Our upvc door is now stuck and will not open. I pushed the handle up in order to lock it the other day, and I felt the locking mechanism 'drop'. When I tried to open it again, it would not open. The door handle now stays in the 'down' position if you press it, whereas before it used to spring up again.
We are completely skint at the moment so any advice on how to fix this on the cheap would be much appreciated!