Usually, if the display manager is not responding, you should check it's related processes by using
ps in a terminal.
You can usually do so by pressing
<CTRL> + <ALT> + <F1> and logging in with your user.
In CentOS, you have 7 ttys available, with 7 being reserved for display manager.
<CTRL> + <ALT> + <F1> through
<CTRL> + <ALT> + <F6> are for terminal use only.
Running only a teminal window gives you the benefit of:
- Not running any GUI (therefore potentially bypassing its problems)
- Checking to see if the system is responsive
- Running diagnostic commands and getting statistics about the system
Once you have logged in, run
ps -eaf and check for your display manager.
If it is there and continues to be unresponsive, you can
Keep in mind, any unsaved work in the GUI will be lost.