Integrate Webcam of Dell Inspiron 3521 is not detected

I have dell inspiron 3521 with windows 7 installed on it.Problem is my webcam is not detected in the device manager,I have installed Dell Webcam Central and skype but both do not find the device.There is no imaging device in dell as there should be. I tried ubuntu too,there also webcam was not detected. I run diagnostics and all tests were passed but still webcam is not detected,its extremely frustrating and only thing I dislike about my laptop. Please tell me how can I fix this? I bought it a month ago it came with ubuntu I installed windows 7,webcam also worked normally then with Skype.