UPVC Window Half Mechanism Permanently Locked???!!!?

Hi,

My UPVC window has suddenly stopped opening. On moving the handle to the open position, only the top locking bolt moves - the bottom one remains fixed. I have already taken the handle off and tried to move the mechanism underneath manually but with no success - it seems to be well and truely stuck.

Does anyone have any idea how I can go about fixing this?

Many Thanks!

H