How to fix “The system is running in low-graphics mode” error?

I am facing “The system is running in low-graphics mode” error on my Dell XPS M 1530 dual boot laptop. I referred How to fix "The system is running in low-graphics mode" error? but not able to fix the problem yet.

I tried

sudo apt-get install --reinstall ubuntu-desktop
sudo reboot

I also verified that greeter is valid.

greeter-session=unity-greeter 

I installed the nvidia driver

sudo apt-get install nvidia-current - More stable/tested version sudo apt-get install nvidia-current-updates - More up-to-date version

Still when I tried to reboot in safe mode it did not help.

if I run startx from command line I see the error Module Nvidia_173 not found. No screens found.

Any thoughts on how can I fix this. Thanks.

Edit: @private: could you please tell how can I verify if nvidia has optimus or not.