Gear box has most likely failed.
To take it out you need to remove the handles (2 screws, 1 may be hidden behind a clip in cap). Then remove the screw holding the locking mechs in place (along the bottom of the window and a few up the sides).
Take photos of the gearbox and look for any names and codes stamped on it. Then google those codes, If that fails email these guys with the pics and codes
http://www.northwesthardware.co.uk/contact.php[/QUOTE]
Thank you Gazman
It's a first floor window and having faffed about with it and consulted my landlord I have admitted defeat and called a repair company in...tomorrow in fact...your diagnosis looks spot on though.
And there's more-- I called a shower called the ABLE GROUP from the yellow pages who were helpful but their first guy couldn't do 1st floor windows??.
So they booked me in with someone else for a 2-4pm visit. I took the afternoon off with no pay and the bugger didn't show up or call.
When I rang the ABLE GROUP they tried to call him 4 times and said he must be driving or on another job. When I expressed my unhappiness at having wasted my time and money I was told 'he does have other jobs to do'
Needless to say I cancelled them.
Just got to go and gaffa the gaps then I will be back on later to get further help for my now diy project