you need a new locking mechanism. on some you can just replace the central gear-box.
there are many kinds and makes. the makers mark will be on the strip e.g. maco, roto etc. these can be bought on-line with steps on how to measure. they are easily removed.
levilewy
March 2010
I can answer this question...
The sleeve that the handle actuates has stretched and does not engage?
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix windows and doors.