Why can't I connect to the network?

I have a small office network with WinXP machines using windows workgroups. One of my co-workers just brought in their laptop and we unplugged one of the workstations and plugged in his laptop but it did not recognize the network. The light on the network card did not light up either. Just kept getting an error “cable is unplugged”. We’ve done this successfully with another laptop but this time it didn’t work. Any thoughts? Thanks.