Q: After installing a new kernel on my CentOS system, the graphics card doesn't use the proprietary Nvidia-driver anymore. What to do?
 
A: From time to time, new kernels are installed. Since the proprietary Nivida drivers are compiled upon installation, a reinstall/recompilation is required everytime the kernel changes. You also need the kernel-headers. All of those should however have benn installed and updated as necessary.

1. If you don't already have a suitable driver available on the Desktop, go to nvidia.com and download the latest linux drivers for your system. Most usually, if you're logged on as root, you should have a suitable driver package on the desktop already.

2. Login as root or open a new terminal window and "su -" to root.

3. Type "init 3" in the terminal window.

4. Login as root again and "cd Desktop".

4.1 Run "yum remove dkms*".

5. Run "sh ./NV<press tab>.

6. On the questions asked, you do not want to download kernel-headers from Nvidia.com, you do want to install 32b-libraries and you do want to have the installer configure your xorg.conf.

7. When back at the prompt, enter "init 5".

8. If you see a fullscreen Nvidia logo, you're done.

9. If you see the wrong screen resolution, login as root and find the "Nvidia X Server Settings tool", somewhere in the menus.

10. The second choice from the top in the tool, should allow you to change the screen resolution. Click Apply, Save to xorg.conf and Quit the tool.

11. Log off and login again. If all looks okay, you're done.

12. Done.

Addendum:

Should the computer already have been rebooted after a kernel update and the Nvidia driver not reinstalled, so that the only thing you see is (usually) iptables output and no graphical screen, just press Control-C to clear the screen and get the login-greeter. Login as root and continue at ยง4 above.