How to kill a process when I cant kill it via the GUI and kill in the terminal?

These days killall will also let you pass in a signal (to save you needing to look up a PID):

killall -9 skype

use this :

kill -9 $(pgrep skype)

To kill a process/application in a Terminal type

$ ps -e | grep skype

this will show the skype process ID

e.g, it shows,

2338 ?        00:00:33 skype

type

$ kill 2338

in GUI configure a short cut key for xKill, (like I have configured to Ctrl + Alt + Bkspace) once you will press the combination, you will get a small cross symbol X instead of mouse cursor .... select the application window with that cross cursor with mouse and it will kill that application.