If a Touch device cannot be detected by a computer (i.e., device serial number doesn't appear in the 3D Systems Touch Setup window),

but the device is known working fine, check the followings:

1. If the supplied USB Ethernet adapter is used, check if the adapter driver is correctly installed. If a computer doesn't have access to Internet, the driver needs to be manually installed. There is a driver installation CD on the bottom of the USB adapter box. Here is an image to show you how the adapter looks like in the Device Manager. 

To open the Device Manager: right click on "Computer" > "Properties" > "Device Manager"

2. Change the order of network cards on your computer. Click here to view the video

3. If wireless is used, take a look at this article: How to use Wired and Wireless connections on the same Windows 7 machine? 

4. If still no luck and the computer has very secured firewalls, make sure UDP 5353 port is open for both incoming and outgoing traffic in firewalls. Here is the instructions on how to open UDP 5353 port for incoming traffic in Windows firewall.