Your GNOME desktop suddenly reverted to TWM in CentOS 5

Has your GNOME desktop suddenly reverted to TWM upon a regular restart? If so, you aren’t alone.

Here is what you need to do to restore your GNOME desktop:

1. Check if you can just get away with switching back to GNOME:

   
   yum install switchdesk
   switchdesk gnome
   

   If that tells you that gnome is not installed then proceed to step 2, otherwise you should have gotten your GNOME back.
    
2. We are going to reinstall GNOME. Run this command:

   
   yum groupinstall "GNOME Desktop Environment"
   

   
   Now run the command to switch desktops:
   

    switchdesk gnome
   
   

   and you should be good getting your GNOME back upon next restart of your xwindow session (Ctrl+Alt+Bcksp).
   
    Original Source from Anton
   http://blog.bordercrossingmedia.com/2009/01/your-gnome-desktop-suddenly-reverted-to-twm-in-centos-5/