Ubuntu 14.04.2 fails to start any graphical interface (unity/gnome)

I am using UBUNTU 14.04 on my lenovo E531 laptop.My problem is: after booting the computer,graphical interface of ubuntu fails to start and it shows a black screen. the one and only way to access ubuntu is by use of terminal commands on the TTY screen (Alt + F1-6). I appreciate any help/guidance in advance.

 i have tried lots of different methods but the problem persists for example 1- i installed gnome shell : http://itsfoss.com/how-to-install-gnome-in-ubuntu-14-04/ but at the end the black screen is all i have 2- I also tried this method ( http://askubuntu.com/questions/41681/blank-screen-after-installing-nvidia-restricted-driver) but it was not helpful again

my Nvidia driver is Nvidia-331, and it was working fine before this problem (i also removed and reinstalled it but nothing happened )