I finally experienced the booting error in Ubuntu, where the screen turns blue and nothing works. I followed the first suggestion here and everything was fine:
- I pressed Crl+Alt+F1 and entered the terminal
- I run
sudo dpkg --configure -aand it told me to restart everything
However, then I have the login screen that does not go forward, being stucked as it appears below. I am still wating for it, however it's been 1 hour since when it started again and I am skeptical that everthing will improve all of a sudden. Moreover the Crl+Alt+F1 after the boot does not work anymore, when I switch it on again. What might be happening?