remove cover plates hiding screws.remove screws.remove screws handle.Insert screwdriver(flathead) of same diameter as square on back of handle & turn.
Good chance not handle but lock mechanism.Gearing snaps and jams.
Www.markcooperglazing.co.uk offers free advice to all in coventry and surrounding areas and has been glazing for 33yrs .
www.markcooperglazing.co.uk, June 2012