I had the same problem and the reason turned out to be that the graphic card was always ON.

What you need to do is to install bumblebee which turns off your graphic card. You can still use it when you need.

Installing Bumblebee

• Open a terminal (Ctrl+Alt+T).


• Run the following commands:

sudo add-apt-repository ppa:bumblebee/stable

sudo apt-get update

sudo apt-get install bumblebee bumblebee-nvidia linux-headers-generic

• Reboot or re-login.

For more information, you can visit the Ubuntu BumbleBee Wiki Page.