Recently, like in the last few months (incidentally, I didn't notice it at first, but I think it might have coincided with the installation of libusb) all webcams have stopped working on my laptop. But, its not a driver error or anything like that, the webcam claims it is working, but when I try to use it in skype, it tells me that it thinks another program is using my webcam. However, I have tried going through every program and closing it until system crash, but it never becomes available. But the light on the side of the inbuilt webcam doesn't come on. And when I added a second webcam, it became available to the system, installed fine, return error 0 on the devices manager, and when I tried to use it, claimed it was in use. How can I find out what might have gone wrong to be causing the system to think that the webcams are constantly in use?
This is most likely a driver issue. You can try cleaning bad drivers (maybe indeed the libusb one you mentioned) using a tool like Drivercleaner. Only downside is that you're supposed to know where to look; it won't tell you where issues are happening.