The first thing to do when this situation occurs is to check the driver. Access Device Manager (Start > Run > devmgmt.msc) and then locate the problematic device. Right click it and select Update driver. If you are connected to the Internet, select the option to check for online drivers. On the other hand, a re-installation will also attempt a possible fix for the camera. Re-install the Dell Webcam Center, but this time choose Run As Administrator. Reboot the computer and you should be able to use the camera.
