This tutorial shows how to install latest nvidia graphics drivers download from nvidia homepage in ubuntu.
If you didn’t installed an old graphics driver in your machine,please skip step4 and step6
Step1: Backup xorg.conf
Use this command in terminal to backup:

sudo cp /etc/X11/xorg.conf /etc/X11/xorg.conf.backup

So,if encounter something error,use following to restore:

sudo cp /etc/X11/xorg.conf.backup /etc/X11/xorg.conf

Step2:Download latest nvidia graphics drivers
Download the latest version from Nvidia download page:http://www.nvidia.com/object/unix.html
By now,the latest version is 190.42,so we can also use this command to download:
For amd64:
wget http://us.download.nvidia.com/XFree86/Linux-x86_64/190.42/NVIDIA-Linux-x86_64-190.42-pkg2.run
For i386:
wget http://us.download.nvidia.com/XFree86/Linux-x86/190.42/NVIDIA-Linux-x86-190.42-pkg1.run
Make this executable(change filename to which you downloaded):

chmod u+x NVIDIA-Linux-x86_64-190.42-pkg2.run

Step3:Install compiling tool

sudo apt-get install linux-headers-$(uname -r) build-essential

Step4: If you have installed an old version graphics driver,search nvidia in “Applications->Ubuntu Software Center->Installed Software” and remove this old driver.Then run this in terminal:

sudo apt-get autoremove

Step5:Close gdm (You need to do following steps in text mode,so you’d better write following code in paper)
Press Ctrl+Alt+F1 key combination and login from tty1.
Tip: Don’t use number pad to input numbers if there are numbers in password,this won’t take effect.
Once login,use this command to close X server:

sudo /etc/init.d/gdm stop

Step6:Delete the remains of old graphics driver

sudo rmmod nvidia
sudo rm -r -f /lib/modules/$(uname -r)/kernel/drivers/video/nvidia

change 2.6.31-14-generic to your ubuntu kernel version

Step7:Install this latest nvidia graphics driver:

sudo ./NVIDIA-Linux-x86_64-190.42-pkg2.run

Accept license and start install

Step8 Restart gdm

sudo /etc/init.d/gdm start

Now,check in System->Preferences->Nvidia X sever settings

nvidia_driver