My MacPro6.1 suddenly cant access wifi or Ethernet whatever I try

My MacPro 6.1 has had repeated problems where it lost network connectivity, both wifi and ethernet. It initially looked as if it was a hardware problem with the interface board that handles all connectivity, and indeed after two thorogh runs at Apple, the machine was changed. And it recurred. Again. It suddenly did it again today and everything i know could not get ethernet or wifi back.. Apple, Tecktool Pro8, varying all the connections to the ports board.. I simply cannot think of anything more to do.. and the ethernet and wifi simply won't connect...what ever i try...

Everything else in my system is fine, and i have, as i had to last two times, revert to my Macro 4.1(firmware flalshed up to 5.1 of course it a stable w chip) which runs as it aways has. faultlessly.

I simply cannot think of any more tests or trials to attempt.

I dont think its Yosemite, its not the boot drive (I've tried several), I'm not sure if it is a interface board interaction with Usb ports(that was the big and unifiiable bugbear in my first two exchanges, confirmed by Apple test at the shop, and avoided by simply not using any USb hubs anymore) even that doesn't work any more.

Everything points (again) to the interface to ports board. so yes, I've tried shutting it all down for several hours as well

I need to get a lot of work finished this sunday and its all on the Pro.. so any brilliant ideas would be ecstatically welcomed... to please try me at ******** on FaceTime if you are struck with a heavenly vision!

<E-mail Edited by Host>