means the drivers are not installed for the device. Is the Ethernet controller built into the motherboard or a PCI card. This is your first challenge. In either case you need to find the make and model of the controller and install the drivers for it.
This is what happens when you/they swap hard drives and do not install all the drivers. Incomplete planning.
I'm pretty much a basic user trying to help my in laws with their dsl installation. Can't connect to internet. Chatted with ATT help and once we went to run/cmd/ ip config..no ip address came back. Went to system/hardware,device manager and had yellow question mark and exclamation point next to Ethernet controller. Recent installed new hardrive on this computer and installed Win 2000. Anyone please help...Old hard drive also had Win 2000 installed using same cd and connected to internet with no problem. Not sure what to do now to resolve issue. Thank you.