Occasionally I've had X Windows lock up solid that no keyboard or mouse input has any effect.
So what do ya do, when X is totally unresponsive? How do ya free your machine?
You have a few options.
Remote ssh Login
If you have ssh installed and have access to another Linux box, you can remote login and kill X. When you ssh into yourbox, it will ask for your password. After entering correct password, do a ps -e| grep X to find Xorg process and kill the process id or run killall Xorg.
ps -e |grep X
6408 tty8 00:08:42 Xorg
That should do it.
Use Magic SysRq Key
You can use Magic SysRq Key to do a System Request and pass keyboard control to the console. Then switch to console and kill X from there. The SysRq key is sometimes marked PrntScn. You have to press
This should allow you to switch to the console by pressing
Once on the console, kill the X Server
If that fails, you have to do a warm reboot then fsck. If you have a current distro and ext3 or equivalent filesystem, you should be okay. Press the reset button and wait for the system to reboot.
Check your X log under /var/log/Xorg.0.log to see what caused the lock up.
# less /var/log/Xorg.0.log