Webcam dont work, keeps saying device not...

Well ive got a webcam built in to my hp laptop (vista) and everytime i try oning my webcam by cyberlink it say 'no video device detected. please plug a video device into your computer' and everytime i try oning webcam on windows live messenger it shows a white screen to my opponent and to me it shows a white screen with the youcam logo n says your captured device is not in or something like that. Is there anything possible for you to do to help me fix this problem please.