Please read entirely the question.
I've decided to write this here because I've seen about 15 questions of the same issue:
Ubuntu not showing up screen, all is black.
Well, let's start in the beggining and finish in the end. The Utopic Unicorn update has caused a lot of issues until now, and more is to come. The black screen is caused by, in real, graphics issues. It has nothing to do with X11, nor X Server, nor GRUB2. And why? Here is the answer.
The Utopic update has changed the way how things work, mainly graphical and performance. And as well, the update has changed the package channels. You don't use anymore the word trusty in sources.list, you use utopic. And updating packages consume time. So, as AMD and Intel have specific dependencies, some of them have not been released for 14.10, for example the linux-headers-3.13.0-37 package. And fglrx, for example, needs it for running well. And as there is no version of it for Utopic, catalyst starts to tumble itself down taking with it the whole system.
But luckily, there is an escape:
You need to purge your driver's package from the system and restore X.Org's original settings.
So, to do that, open the tty1 terminal ( Ctrl+Alt+F1 ) and do the following:
If you are using nvidia:
sudo apt-get purge NVidia-*
If you are using Intel:
sudo apt-get install --reinstall xserver-xorg-video-intel
And, if you are using AMD:
sudo apt-get purge fglrx-*
The system itself will feel something is missing, and so will fix itself. Then, go on and type:
reboot
Hope that it helped. And sorry if I made any mistake, if this was the case, be sure to hit the Edit button and fix it.
