Help I can't close my double glazed window!?

Please can anyone offer advice: I just opened one of our UPVC windows and now it won't close - I guess it must have dropped somehow because the top locking mechanism is fouling on the frame when I try to pull it closed. The windows were only fitted last summer, but I can't get hold of the company - it being Sunday - and of course my husband is away. I am really hoping there is a simple screw adjustment I can make to pull the top half of the window back towards the hinge - is this possible and what should I look for? Many thanks