How can I debug a webcam issue if
- the event viewer doesn't show any errors concerning WIA or camera/hardware topics
- WIA is started and restarting it causes no errors/warnings in the event log (actually no events except from the SCM)
- Windows (Devices and Printers) shows the cameras and doesn't indicate any issues
- Programs using the camera like Skype will indicate there is a camera connected but will not show an image from the camera
- the issue occurs with a USB-attached external webcam for a PS3 as well as the builtin laptop camera (also on the USB bus)
I systematically went through those things and there is no indication of an error. Since the external camera works on another device, I am left thinking that there is a software issue. First hunch was that WIA was disabled or failed to start. I could falsify that. Right now I'm out of ideas. The software side seems to be the culprit, but it's also the side that doesn't indicate an error, which belies the result. On the other hand at least the external webcam has been checked on another host and works fine.
What else can I check?