The only thing that has changed recently is the mounting: the old 3-legged base was worn out and would not hold position any longer, so I removed the camera unit from it's base and mounted it on a wire frame slightly above my monitor. It did work a few times since I did this, but since this was a recent change I thought I'd include it.
I have tried rebooting the computer, plugging the camera (with Trackclip Pro and without) into different UBS ports, downloaded the latest software (uninstalled the previous) to no avail. I have checked the Device Manager but I cannot tell which USB device is which. Here is a screen shot of the device manager:
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Has my TrackIR finally bit the dust? Thanks for your replies.