Z77X-UD3H breaks network

[Uncle_Steve]

So, this is the one of the craziest things I've ever encountered.

I built a new box for my son based around the Z77X-UD3H. All seems
well EXCEPT that sometimes when it's turned OFF(!) it breaks the
network. All I can do when that happens is to turn his system on or
disconnect it from the net. (By "breaks" I mean if it's plugged in
nothing else works. As soon as I unplug it, everything is fine again.)

I've tried different cables and switches. It's definitely his computer.

I'm going to try and set things up so that I can do a tcpdump when
this happens again, but in the meantime...

Any ideas anyone?

Thanks.

[Uncle_Steve]

It happened just seconds after my first post. Unfortunately, tcpdump didn't show anything weird. Just all of the sudden everybody went amnesiac and started issuing ARP requests... who has blah blah. As soon as I disconnect the z77, things are fine.

[Benz]

It could be a BIOS issue or a LAN card itself. Try updating your BIOS to the latest version and report back.

[Uncle_Steve]

It could be a BIOS issue or a LAN card itself. Try updating your BIOS to the latest version and report back.

Running the latest BIOS. Decided to cut my losses; dropped an Intel PCI-E NIC in and am using it instead of the NIC on the motherboard itself. If this was my personal system, I'd probably investigate longer, but it's a gift for my son; not much of a gift if I'm screwing around diagnosing this weird problem.