If you are unable to return to the FreeNAS Web GUI after making changes, re-attach a keyboard to the FreeNAS box and reboot (soft or hard reset) with the FreeNAS LiveUSB still plugged in.
Then, once FreeNAS has booted (after 2-3 minutes):
- Press 4
- Press left arrow
- Press Enter
This needs to be done in exactly this order, with each key pressed just once. This resets the FreeNAS box to defaults, and then reboots FreeNAS as it was before any configuration was done.
After a further 2-3 minutes, you should be able to reconfigure FreeNAS (from the beginning again). Once you reconfigure the network interface and assign an IP to allow access via the WebGUI, you can then restore your previously saved configuration.
If this does not work, re-attach a monitor to help you select the correct options.