Bulit-in webcam shows a black screen everytime i try to use it.

I have a sony vaio NW series Notebook with Vista. The webcam was working before, but not it was not for about 2-3 weeks. When i try to webcam on MSN it doesn't let me and when I try to take a new profile picture either on MSN or Facebook, it jus shows a black screen as well. Can anyone help me fix this problem please? Thank you.

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