It could be the drivers for the camera were corrupted when another driver for something else was installed. Have you installed anything recently that might have caused a conflict with your Vivitar Vivicam?
The BEST course of action is to try installing the drivers on another machine, then hooking up your Vivitar Vivicam to that machine.
If it works, you know the camera is OK. If it doesn't, you know the camera is probably bad.
If it works on the other machine, then it might be time to remove and re-install the drivers for your vivicam on the main machine.
If that still doesn't work, you could try going back to an earlier restore point, one that was made before this problem started.
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