Webcam driver stops working during regular PC operation.
If the Web cam was Generic, or even Brand name, and it came with a Drivers disc (this would mean that it is not plug and play), try completely uninstalling the Driver software for the web cam. After the uninstall has finished, reinstall the drivers, taking extra care to follow ALL on screen instructions to the T. If at some point there were other web cams, and the drivers that belonged to those cams installed on the computer, be sure to fully uninstall all of them. Only use the cam and the drivers that you are attempting to install. After all of that, the cam should work just fine.
If for some reason the cam does not work after reinstalling the drivers, try a different brand of web cam. The computer that the drivers are attempting to operate on may not be adequate to support those drivers. If that's the case, try a generic, cheaper web cam as I said.
Also: While powering up the cam, don't run anything unnecessary.
Hope this helps.