I have lost my GNOME Desktop environment twice now, so I thought it's time to write down how I managed to get it back. It happened like this: On my old computer, which I primarily use for backups, I decided to remove all the applications I didn't really need.
I thought that by using the GNOME Add/Remove Software menu function and only removing optional packages from the GNOME Package Manager's Applications section, I'd be on the safe side.
GNOME Package Manager
This turned out to be wrong: after removing all the unused applications in, I logged out of my GNOME session, and when I tried to log back in, I only got an ugly TWM session! Apparently, I had removed a crucial piece of the GNOME Desktop environment...
Prerequisites
The yum program is still installed on your computer.
Procedure
Open a root shell, or use the sudo function for the following steps.
To reinstall the missing parts of the GNOME Desktop environment, enter the following command: yum -y groupinstall "GNOME Desktop Environment"
This step might not be necessary, but it can't hurt: Restart your computer.