Will not release TCP/IP

Windows 2000 station connected to Netgear Router. All stations set to obtain IP address automatically and work fine with one exception. Station is using a TCP/IP address from “somewhere” and I cannot find. Have deleted all LAN settings and rebooted many times. This will allow me to setup TCP/IP to attach to LAN and internet, but upon reboot reverts to “ghost” TCP/IP address. I can I permanently correct this?