There's a good chance that you may need to replace your window hinges. There's some good tips for diagnosis at the bottom of this page: http://www.handlesandhinges.co.uk/html/window_hinges.html
Janet, handlesandhinges.co.uk
March 2010
Automatic Answer
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howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix windows and doors.