In order to fix the issue, press Alt + Ctrl + Delete key combination, open Task Manager and close all unnecessary programs that may use your webcam. If it doesn't help, I suggest you update your webcam drivers. For this purpose, navigate to Acer Drivers and Manuals page, identify your computer model, select your operating system and download the latest files available. After that, press Windows + R key combination, type devmgmt.msc and click OK. Expand the Imaging devices list, right-click on the webcam driver and select Update Driver Software. Use the Browse option to navigate to the installation package, select the driver and install it following the on-screen instructions. If you still have issues, check the troubleshooting guides provided by Yahoo.