Let`s consider possible issues.
Before connecting your camera to computer, make sure that there is no external damage. You should check connection cable and device itself.
If you use external webcam, you need to check cable connection to computer and also check that cable is properly connected to your camera.
Change connection port. Webcams are often connected via USB. If it does not work, you can try to reconnect to another one. If situation has not changed and webcam still does not work, issue may be with USB ports or camera itself.
Some devices are equipped with a special privacy shutter, which allows you not to worry about your privacy when you don't use camera.
If it so, check if shutter is open.
If you have connected a camera but cannot use it, we recommend that you check it with Device Manager and make sure that your operating system has detected webcam.
Then, from entire list of categories, you should find Cameras, Imaging Devices or Sound video and game controllers and expand them.
If you could not find the device in manager, this may mean that your webcam is damaged or not compatible with operating system.
If there is a yellow exclamation mark next to your webcam name, then there are some issues, most likely with software. You need to install or update driver for device.
In some cases, you can see a gray arrow icon next to webcam name.
This means that the device is detected by operating system, but it is turned off programmatically. To enable it, right-click on its name and select Enable device.
If you have multiple webcams connected to your computer, usually applications or online services provide opportunity to select necessary device. Often, to do this, you need to go to a special menu in program settings and make your selection.
If there is no such menu, or you cannot find it, you can select a desired camera in settings of operating system:
In the opened window expand Cameras, Imaging Devices or Sound video and game controllers categories and find your cameras in them.
You will need to turn off all devices except the one you want to use. To do this, right-click on camera and select Disable device.
In some cases, operating system does not allow access to webcam. You need to change privacy settings to fix this issue.
Usually, webcam can only be used by one application. If it does not work in a desired one, you need to make sure that device is not being used by another program.