network connections

winXP Pro, when I connect a specific workstation into network hub, network connections become disabled. I’m using a 4 port hub for a small network, two workstations work great, connections are up and running with just those two… when either of the other two connect, within two minutes the entire network does not exist… all settings are identical in a workgroup setting, all receive the same zone and subnet mask with an auto assigned IP.
How can I get this network up completely, what is wrong with the two machines that kill the connection?