I ran into a problem this week, where I couldn't find a solution to.
Everytime I start Ubuntu, it boots nominally, until it reaches "starting Gnome Display Manager" where the Konsole gets stuck and the screen is going black every few seconds.
I also cannot access any tty by pressing Ctrl + Alt + F1, F2
I found an older question, where they solved the problem by reinstalling a new Nvidia Graphics driver.
I can't try that, because I can't access a shell, and my Ubuntu runs fully on Intel Graphics. (Lenovo Ultrabook)
Can I still use my Ubuntu, or do I have to wipe the partition?