Go through these steps.
https://docs.duet3d.com/en/User_manual/Troubleshooting/Duet_wont_respond
You can d a full firmware wipe and get the board to appear as a port in BOSSA in order to reflash the firmware (from a fresh download) and try YAT again.
https://docs.duet3d.com/en/How_to_guides/Getting_connected/Getting_connected_to_your_Duet