LightDM does not appear after installing a driver from Additional Drivers

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http://askubuntu.com – I simply was looking at the default drivers it gave me (under System Settings->Additional Drivers) and I selected version 96 and activated it. After it installed it asked me to restart, and I did. Now it will not boot back up; the problem is that LightDM will not come up. I am new to Ubuntu, and I need to know a command to shut down all drivers or something. (HowTos)