Hey when simple nearby lightning bolt can knock out PCsOverblown. (You need to buy an UPS to solve your problem with EMI/brownouts caused by powerline 'sags'.)
The close lightning bolt induces saturation current in the LAN cabling. CAT5 cabling is unshielded. The differential signal elimates noise problems as long as noise signals are within certain specs. A lightning bolt or an EMP far exceeds the few volt limit and saturates the clamping protection diodes on the circuitries input stages. These gates are then permanently shorted.
Device is now useless.