Windows Vista Power dvd not working ?

Hi i have recently done somthing to my computer. Dvd's will not play on my pc running windows vista. They normally start playing soon as i put dvd in but won't now. I have done a system restore. They still won't work When i click on the dvd to play- nothing happens. Can anyone tell me what i might of done and how i can put it right
cheers!

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hi when i put the dvd in the tray go to my power dvd icon click it then i see the picture of the film in the lefy of the screen double click it just closes power dvd down i have tryed other ways aswell still does the same
the dvd's are normal dvd' ie films