Router disconnects when changing screen res

I have a problem with a router disconnecting when changing the
resolution of the monitor...?!?!

It's not the router as I've tried both a Netgear and a Linksys. It
took a while to nail it down to screen res but I can reproduce it each
time now. I've tried most things such as changing filters, updating
firmware, updating my boards BIOS, installing chipset and ethernet
drivers etc.

My PC is an AMD x2 4800 with two Nvidia 7800's running in SLI mode and
I have applied both the AMD processor driver and the MS Hotfix. It's
running SP2.

Only connection I can think of is that my machine has problems running
in SLI mode - it claims there is no cable connecting the cards
although there is.

Has anyone *ever* seen a problem like this? It's bizarre!

Thanks