My computer wont shutdown

Question

If I try to shutdown my computer it simply takes me back to the login-screen. I looked around and found :

Type in terminal:

1. sudo gedit /etc/default/grub
2. Find the line: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
3. Change this to:GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=force"
4. Save the file and close the file.
5. Finally, in terminal: sudo update-grub

But now there is a new problem when I try step 5 it says:

*myname*@ubuntu:~$ sudo update-grub
[sudo] password for *myname*: 
/usr/sbin/grub-probe: error: cannot find a device for / (is /dev mounted?).
*myname*@ubuntu:~$ 

I am new whit linux and dont know what to do.

Answer 1

Have you tried to shut it down from the Terminal?

sudo shutdown -P 1

(Also, try to use some Formatting when Posting here, so your Question is more Readable ;-)

Answer 2

Adjusting the Grub worked for me great.

sudo shutdown only reset my system until I adjusted the Grub and then it worked great.

I did the above steps you have done then I removed acpi=force from GRUB_CMDLINE_LINUX_DEFAULT and added it to GRUB_CMDLINE_LINUX instead, (i.e. GRUB_CMDLINE_LINUX="acpi=force").

Then I shut down the computer, using the power button to power off after it stopped shutting down at the black screen with a series of messages that ended with "[end trance ...]" as it did before (I had GRUB_CMDLINE_LINUX_DEFAULT="" to show messages instead of the splash screen). After re-booting, shutdown worked correctly.