window has expanded?

plastic does expand.
it sounds like a top opener though.
the common fault is when the fitter packs the glass unit they put the packers away from the corners meaning the weight of the glass pushes down on the middle of the sash making it bow down preventing it from working.
if you take the bead out and move the packers to the corners this will mean the glass unit will be supported.
and if you open the sash loosen the screws on the sides push the sash up about 5mm then lock the scews this will also work.

midas
October 2010

PVC doesn't expand like timber.
Have you checked the hinge screws are tight?
And are the locking plates on the frame all in the right position?
It's difficult to advise without knowing the window, lock, and hinge type, but if it fit correctly when it was installed, then there's a problem with the hardware which can be corrected by process of elimination.

Big Softy
October 2010