LAN connection causes shutdown

I have just replaced motherboard & processor
Mobo = ECS Elite K8M800-M2

Everything works fine ntil....I try to connect the LAN.

I insert the ethernet cable and start the PC, all runs ok for a few
minutes - or until I try to open IE - then the computer just shuts down - no
freezing, no blue screen, just shutdown.

Whatsmore, I have to wait 5-10 mins before it will start again, hitting the
on button before then results in nothing whatsoever.

If I take the ethernet cable out and re-start, everything works OK

Any ideas anyone?????


Ron