Please send M115 and check whether the response includes "+ DueX5". If it doesn't, then the Duet isn't seeing the DueX5. This can be caused by the 50-way ribbon cable not being plugged in securely to both boards, or by a faulty ribbon cable. However, the most common reason is a particular intermittent fault on the DueX5. So if the ribbon cable is securely plugged in at both ends, please return the DueX5 and ribbon cable to your supplier.
The Ethernet is a separate issue. Make sure that you have enabled the network using M552 S1 (which you can do in config.g) and verify it is enabled by sending M552 (as you have done). Then try connecting it to different devices (e.g. router, or Ethernet port on a laptop or PC) using different Ethernet cables, to see if you can get the link LEDs to light up on the Ethernet sockets of the Duet and the other device. Once you have the link LEDs lit, we can look at configuring the Duet to make it visible on the network.
