Although Linux is a really stable platform, there will be some times that a program will freeze. In those cases most people are stuck on what to do.
Generally you have two choices for closing a stuck program:
1. Close all programs related to that program (including multiple windows of the program)
2. Close a program with your mouse cursor.
Use the KillAll feature to kill a program.
1. Press Alt+F2 and type in gnome-terminal to open a terminal session.
2. Inside of the terminal type in sudo killall . For example, to kill firefox type in sudo killall firefox.
Use the xkill feature to kill a program you click on
1. Press Alt+F2 and type in gnome-terminal to open a terminal session.
2. Inside of the terminal type in sudo xkill; then click on any window to kill it. This command makes your cursor act like a terminator, deadly.