Some programs will hijack your webcam and not release it for other applications. Make sure all applications such as Skype and VID are turned off, as well as any webcam programs you may have like YouCam or MagicCam. Sometimes these programs are in your Start-up menu so rebooting doesn't work, you have to manually close them. If you recently used a webcam program and deleted it, it is possible that it hijacked your webcam and is not completely removed. I like using CCleaner to completely uninstall programs. Without knowing more details on your situation this is where I would start.
Check if you have any programs running that could be using/locking your webcam. Just close everything you don't need. If that does not help, you can also try a webcam sharing application, like SplitCam. That makes your webcam available to multiple programs, so never a sharing issue.
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Some programs will hijack your webcam and not release it for other applications. Make sure all applications such as Skype and VID are turned off, as well as any webcam programs you may have like YouCam or MagicCam. Sometimes these programs are in your Start-up menu so rebooting doesn't work, you have to manually close them. If you recently used a webcam program and deleted it, it is possible that it hijacked your webcam and is not completely removed. I like using CCleaner to completely uninstall programs. Without knowing more details on your situation this is where I would start.
Check if you have any programs running that could be using/locking your webcam. Just close everything you don't need.
If that does not help, you can also try a webcam sharing application, like SplitCam. That makes your webcam available to multiple programs, so never a sharing issue.