The system is running in low-graphics mode is the message I received after my laptop froze when I upgraded to ubuntun 14.04 I need this sorted been on google search all day and im not winning please help need to get my laptom running
Try the following:
When you hit the log on screen type ctrlaltF1 to open a tty1 session.
Log in with your username and password.
See if that solves your problem.
To clarify more on Musher's answer, it is a problem with Ubuntu's default display, as lightdm is being obsolete and unsupported. To fix this press Ctrl + Alt + F1 to open a temporary display-lacking terminal. If that doesn't work use Ctrl + Alt + F3 instead. Once there, there are a two options to solve lightdm.
1: Use GDM Instead RECCOMENDED
Then select GDM and hit Enter.
2: Repair LightDm NOT RECCOMENDED