If the ETN21 card is new, confirm connection by running the DOS command Ping at default 192.168.250.x (x being the node No. in front of the card).
If you get an answer, run Internet Explorer the address http://192.168.250.x to view the card details using its web server interface, using the password ETHERNET.
If you do not get any response to Ping, check the connections. If you do not know the IP address previously configured, in this case you must connect via a serial ports to read / change the IP address. If the Ping works but you are unable to connect CX-Programmer, make sure the No. node in front of the card ETN21 (Hex coding) is identical to the last field of IP address (coded decimal).