I have routine updated ubuntu 12.04 LTS 64 bit. I have dual os: windows 7 and ubuntu 12.04 LTS 64 bit. Grub is working fine. Windows 7 is also working fine. I have installed from a CD downloaded from ubuntu site. I have updated my 12.04 successfully in last few months. I did routine update on 12.04 as usual and it asked me to restart to complete update. I restarted and arrive at a signon screen which has my username and "Guest". This screen shows the menu at the top with power, time, calendar, etc. So I entered my password and I am taken to a screen which only shows a blank screen, empty launcher area only including dash and trash. The only thing that works is I cam move my mouse but there is nothing on screen which I can click. Terminal is also not working using Alt+Ctrl+T key. Please help in this.