I can no longer start my computer

[nicrnicr]

Dear all,

As I couldn't shut down my computer with the mouse, I wrote

sudo shutdown -h now

in the terminal. Now, when I start the computer, I can choose the Kubuntu 16.04 partition but nothing happens. There is a black screen with a white cross which blinks on the top left.
Please, what could I do?

[GreyGeek]

When does the black screen appear? Right after you choose the first (default) line in the grub menu, and before the login screen appears, or after you log in?

[nicrnicr]

Thank you GreyGeek for your answer. The black screen appears right after I choosed the first (default) line in the grub menu. I never have had to login to use Kubuntu.
.
It may be helpfull to precise that this black screen with a white cross which blinks already appeared a few seconds after I wrote

sudo shutdown -h now

The computer turned off just after.

[nicrnicr]

When I try the recovery mode, login and password are asked and then the screen is like a terminal. I don't know what to do.

[GreyGeek]

It appears that you have set your login to be automatic, and that the xserver didn't start or crashed. The usual cure is to delete the file "/home/youracct/.Xauthority", which is probably owned by root.
From the recovery menu choose to log in as root in a terminal. CD to your home account and issue
rm ~/.Xauthority
Then
reboot

It is because of this problem, which rarely occurs, I never use automatic login. If the login to the desktop fails it will throw you back to the login prompt. There you can do an Alt+Ctl+F2 to get a console screen from which you can log into a terminal and issue the command
sudo rm ~/.Xauthority
then exit the terminal back to the login screen and then log in. The .Xauthority file, which should be owned by youurname:yourname, will be automatically recreated with you as the owner.

[nicrnicr]

Thank you very much GreyGeek but thought I deleted .Xauthority as you wrote me after having choosed the recovery mode and after login, I can still not start normally. I still have the black screen with a white cross which blinks after I choosed the partition and after Kubuntu has been written in the middle of the screen.

[GreyGeek]

I can no longer start my computer

Can you bring up a terminal by using Ctl+Alt+F2 ?

[nicrnicr]

Thank you GreyGeek. Yes, I can have a terminal by using Ctl+Alt+F2 when the screen is dark with the white cross which blinks. And I can login. Please, what should I do?

[GreyGeek]

That you have a terminal suggests that either the xserver is broken or KDE is broken or not firing.
In the terminal log into your home account and issue
startkde

If that doesn't work then issue
startx

[nicrnicr]

Thank you GreyGeek.
After I wrote

startkde

, the computer answered

The software "startkde" is not installed. You can install it by writing "sudo apt install plasma-workspace"

.
I wrote what the computer proposed me and I wrote startkde again. The answer was then:

$Display is not set or cannot connect to the X server.

.
Thereafter I wrote startx and the answer has been

~/.Xauthority does not exist
usr/bin/X: not found
Xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error

[GreyGeek]

Try
sudo modprobe i915
And try startx or startkde again

[nicrnicr]

Thank you GreyGeek, but:
The only thing which happens after I wrote

sudo modprobe i915

is that my password is asked.
When I write startkde, I have the same answers as in #10.
When I write startx, the computer answers:

/etc/X11/xinit/xserverrc: 3: exec: /usr/bin/X: not found
Xinit: giving up
xinit: unable to connect to X server: Connection refused
xinit: server error

[GreyGeek]

It appears that the hard reset killed some of your root system files.

You could continue trying to fix things by first trying the fsck option on the grub recovery menu, reinstalling the Xserver package you were using, and redoing suggestions above. Total time: hour(s) to days

OR, boot a LiveUSB, mount your HD Linux partition and copy your important data files to another USB stick. Then, reinstall Kubuntu and copy your data back to your home account. Total time: an hour or less.

Recommendation: When you get to the installation part where you are asked what filesystem to use it will default to EXT4. Change that to Btrfs.

After you finish and reboot come back to this forum and search for Oshunluver & Btrfs. You’ll be able to bkup your system in seconds and restore from a fiasco like this in under 5 minutes.

[nicrnicr]

Thank you very much GreyGeek for your explanations!
When I prepare the new installation of Kubuntu 16.04, I don't have the possibility to choose the filesystem. Where we want to install Kubuntu 16.04, there is already Kubuntu 16.04 and for the computer there is no question such as "Which filesystem?". I can choose the filesystem only if I delete the existing Kubuntu 16.04 or if I install the new one on a virgin part of the HDD. Please, should I delete my existing Kubuntu 16.04 or do something else?

[nicrnicr]

I suppose that if I install again Kubuntu 16.04 on it (and without the choice of the filesystem), it could repair it, but I'm not sure.