you need to reinstall TCP/IP and Client for Microsoft Networks...
those are required to be on a network and to log on to a Domain Controller.
If you still can't log on to the domain, go into the command prompt and type ipconfig...if your IP starts with 169.xxx.xxx.xxx, then you are not getting an IP from the DHCP server and there is probably a hardware failure. If you have an IP, see if you can ping the domain controller.
EP, glad to see you come back and tidy up...did want to ask a one day favor, I want to enhance my resume , was hoping you could make me administrator for a day, if so, take me right off since I won't be here to do anything, and don't know the slightest about the board, but it would be nice putting "served administrator osnn", if can do, THANKS