old PVC windows - problems opening/closing

Hi
house with old PVC windows. Some of them don't open at all, and now I'm having problems with some of the others. I can open them, but they are difficult to close (and in this cold weather!) as they seem to be sticking on the plastic panel the catch is supposed to slide over. To be precise, the handle seems not to have enough gap to go over the panel.

So does anyone know :
How I can open the ones that just won't? I'm afraid I'll snap the handle if I use too much force.
And what can I do to prevent the problem with closing the ones that do open?

Thanks in advance! I hope I've explained this well enough as I've no idea what the technical terms might be.

Have you tried to make contact with a supplier / manufacturer of PVC windows ?? Normally they will inspect the work and provide you with an estimate. What part of the country are you in ??

Would the ones that won't open be locked by any chance? Some of our old windows stopped opening but it wasn't because they were locked.

The hinges are probably the problem with the ones that don't close.

You don't state where you are but we had a recommendation for this repair guy some time back.

There are also some previous threads on this subject.

Sounds like the time for new windows but if you can't afford them at the moment it might well be worth your while to get them repaired. A friend's mother paid a fair few bob to get theirs serviced (for want of a better word) and it made all the difference to the heat in the house.

Thanks for that, mercman & SueEllen.
The windows came with the house and as I'm extended on the mortgage, we won't be replacing them for a while yet
I don't think they are locked. There is a button on the handle, but I don't know what for because you don't need to press it to move the handle. They are old (going cream-coloured) so I'll look into getting someone to look at them. Thanks, that was quick!