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Yesterday i install gdm and set it default display manager then l notice ubuntu is running but there is several lines appear on desktop when i want to shutdown system after i powered off system and start Grub Menu appear and normal boot system but nothing is appear and black screen is regularly appear even after several restart.

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marked as duplicate by karel, Seth Mar 13 '14 at 0:32

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

    
The questions which this is marked as a duplicate of are: 1. A very, very lengthy page about boot issues of all sorts, mainly grub problems 2. A page on how to switch back to lightdm if you've made gdm your default display manager. Neither of them answer the question, which is "why is GDM showing a black screen instead of the usual login screen". Also the only answer below is also just info on how to switch back. – Damon Smith Oct 4 '15 at 22:14

Try this:

on that black screen click Ctrl+Alt+f1

enter your user-name

password:your password

$ sudo su

enter your password

run

# dpkg-reconfigure gdm

or

# dpkg-reconfigure lightdm

and choose lightdm

reboot

(sorry for my bad English)

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1  
can you try to use proper formatting please? I have no idea what you're recommending. – Seth Mar 13 '14 at 0:32
    
CTRL+ALT+Fx just yields a blank black screen with a blinking cursor in the top-left, no login prompt, no response. – Jonathan Neufeld Nov 5 '15 at 6:21

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