Webcam not working with Windows Live Messenger

I have a hp webcam and it has been working all day and i've had it for over a year. About half an hour ago I was in a video call, then 5 minutes later I tried a video call with someone else but my webcam wasn't working. On Messenger I went on to tools>audio and video settings and it was fine and I could see myself. Even when I went on the program for my webcam I could see myself. But when I go into video call it shows a red cross on my laptop and others computers/laptops. I have signed out of messenger and rebooted the laptop but still no success. Please help. All help appreciated.