Ubuntu Lubuntu 12.04 Shutdown doesn't power off [Solved]

I found that Ubuntu 12.04 and it's family (Lubuntu Xubuntu Kubuntu 12.04) does not power off when I Shutdown or Reboot my PC. When I press shutdown button it kills all running processes and the screen goes black but my computer doesn't power off. Machine's fans are still running and the screen is still on. It stop at the screen shows below.

Shutdown doesn't power off 

I have to hold down the power button in order to completely shut down my PC. It seems all processes are stop working, but a blue dot under logo is still on and nothing happened afterwards.

• sudo gedit /etc/default/grub
• Now find the line: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
• Change this line to: GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=force"
Save the file and close the file. Finally, in terminal, type:
• sudo update-grub

To implement commands you must press 'ENTER' button of your keyboard after each command. This command has been solve my problem.
Remember that at first line 'gedit' is a name of text editor. So if you are in Lubuntu change 'gedit' and write 'leafpad' to open grub configuration file. Do the same for other Linux distro.