There are times when a program freezes and hangs up. It wont respond to any mouse clicks or keyboard. Then you can terminate that program using Windows Task Manager.
You can start Task Manager in many ways. One keyboard shortcut is Ctrl + Shift + Esc. You can also start Task Manager by right clicking on the taskbar and selecting Task Manager as shown in the image below :
In the Task Manager, look for the process that is frozen. Select it by clicking on it. Then right-click and select End Process as shown in the image below. In the attached image opera.exe (which is Opera browser’s process) is being terminated.