As cannot get to Desktop again when running sudo lightdm tty shell prompt, wondered could be caused by some previous failed initializartion, so need to know where the startup log file is put in directory
Please help point it and show a brief tips to understand that log file so that'd fix te startup to log into desktop smoothly
If not started as a service they are either in /var/log/lightdm/lightdm*.log or in the syslog where you will have to grep 'lightdm'.