As Gerry said, you should run the Utility tool and check if the network parameters are set properly.
And ofcourse the first thing to do is to setup the network which is basicly to set the IP address and subnet mask of the network adapter in your computer to match the IP address of the UC400ETH.
The Utility tool communicates with broadcast messages, so it will find the UC400ETH anywhere on the LAN even if it is totally missconfigured to the network adapter,
and the utility tool will tell you if the IP settings are correct or not.
Here is a video which covers the setup procedure really well. The video was about the UC300ETH, but the UC400ETH works exactly the same, so the video is the same useful for the UC400ETH too:
https://www.youtube.com/watch?v=eaq7DScSz9oTalking about mini computers, even this 75mmx75mm (3x3inches) size pico-ITX computer can run the UCCNC without problems:
http://shop.cncdrive.com/index.php?productID=820