PC hangs during post when webcam is plugged in

Really there are only two options here. Either the BIOS is buggy as suggested in the link provided in the comment section by @NetworkKingPin, or else the USB webcam doesn't meet USB specifications as built and is causing a short.

I'm personally in favor of the latter interpretation, as it would also explain why the webcam is occasionally freezing your system during Windows operation.

The test of this theory is simple - get another webcam and test things with that. If the problem persists, there may be a short occurring with the hub, or the port in which the hub is installed. Changing hubs and moving ports may also resolve the issue.