Stuck UPVC window

[speedmachine]

One of my UPVC double glazed windows is stuck. When I turn the handle the bolt at the top of the window opens but the one at the bottom doesn't. I can tell this by trying to puch the window open which shows that only the top is lose. It's not a large window.
It should still be under warranty but I'm having trouble getting hold of the company that fitted it.

Can I repair this my self by removing the glass? Will the bolt be accesible by removing the glass?

Any tips?

[h4rvy]

No - the bolt / locking mechanism is on the outer part of the opening window.