Cannot reboot/shutdown Ubuntu 16.04

I hadn't any problem with 14.04, but 16.04 is so buggy. I can't reboot Ubuntu after installation is completed from live USB/DVD and I must press the power button. Also sudo reboot and sudo poweroff don't work when Ubuntu is booted. I updated Ubuntu but the problem still exists.

Solution 1:

OK. The first problem (reboot problem after installation was completed) occurred because I set acpi=off during the installation because Ubuntu got stuck in loading purple screen. After many tries I could pass by the purple screen by chance without setting acpi=off! Then after installation, Ubuntu was restarted without any problem.

The second problem (shutdown and restart problem after Ubuntu was booted for the first time from hard disk) was because of Nvidia driver. I did

sudo apt-get update
sudo apt-get upgrade
sudo apt-get dist-upgrade
sudo ubuntu-drivers devices
sudo apt-get install nvidia-361

And now everything is fine :-)

UPDATE

As I said I could not pass by the purple screen during the installation and I found what the problem was. I had connected a USB 2.0 flash drive to a USB 3.0 port for installing Ubuntu. Today I connected a USB 3.0 flash drive to the USB 3.0 port and I booted Ubuntu with that and the problem was solved (I don't need to wait for a chance or set acpi=off to boot Ubuntu). But unfortunately I am getting a new problem and it is I cannot reboot or shutdown Ubuntu .