Hmm, we never had the case that a unit totally stopped working.
What does dmesg show up when plugging in the device?
Check the USB Port, if you totally cannot get it work anywhere ship it back and we will investigate what happened, we would be curious what happened because we never had a new device just stop to work. Even in the worst case dmesg has to show up something. The USB Chip always has to respond with something at least.