This question already has an answer here:

I got Ubuntu 12.04 up and running with all the latest updates and everything was fine until I decided to install the recommended Nvidia drivers from the Addtional Drivers application.

After rebooting and logging in Unity won't load properly. The desktop loads really slow and simple things like clicking on the Unity menu in the top left corner now take ages to register.

At first I thought something went wrong during the installation, so I popped in my USB flash drive, formatted the Ubuntu partition and reinstalled it. Once it was done I tried installing the recommended Nvidia drivers again and the same issue appeared.

My system specs are an Intel Core 2 Duo E6750 CPU with 2GB of RAM and a GeForce 8800GTS graphics card.

merged by fossfreedom Feb 16 '13 at 11:22

This question was merged with What should I do when Ubuntu freezes? because it is an exact duplicate of that question.