I'm had the exact same issue for some time now , it happens intermittently and to random machines just after you get to the login screen. Only happens when on network & if you leave network cable out until login screen then it logs in ok.
I've tried everything i can think of , reimaged , updated drivers for NIC , installed second NIC , removed / readded from domain , re-registered dns..checked event logs on server , everything else you can think of...
It even happened to a VM and also to a brand new reimaged PC as soon as it was plugged into network..
Anyone have any thoughts ?