The article I’ve linked to below wasn’t written by me but is something worth noting for when things go wrong with your pfSense. My only thoughts to complement this article is to use Linux with the “minicom” command line tool to gain access to the pfSense firewall (using a USB to USB-Mini-B) and also (go back in time and) have a backup of a working config on a USB disk attached to the pfSense firewall.
Just FYI, the minicom command to use is (something like):
sudo minicom --device /dev/ttyUSB0
If you can’t type anything, press the following key combination:
"Control+A" and then "e".
Or you can use the “screen” command (as documented) like this:
screen /dev/ttyUSB0 115200