I'm not really experienced with Ubuntu and do not have a clue what to do in the current situation.
My system currently has two boot states:
Does not boot at all. Going to different console by ctrl+alt+f2 shows that it tries to start Snappy daemon in the loop. It waits for it to be started for 90 seconds, then stops it and tries to start again.
Fails to start GUI, but different console ctrl+alt+f2 loads terminal where I can execute commands. I'm not sure exactly how to go into that state from the first one. Perhaps by pressing Ctrl+C several times sometimes helps after restart.
In the second state it complains about:
WARNING: IceLockAuthFile failed: File exists
I found this Debian bug report and tried to delete
/var/lib/gdm3/.ICE* and then restart the system as suggested there, but this returns me to the first state.
Ubuntu version 18.04 LTS