How to stop application that freezed and locked task manager?

Try telling the Task Manager to always be on top.

1. Open up the Task Manager before you start your application/game.
2. Click "Options" ("Možnosti" in the picture below)
3. Check "Always on top" ("Vždy navrchu" in the picture below)

Next time you should be able to view it. Also try Alt-Tab-ing out of the app/game, so the focus is on something different.

I tested it on Windows 8 on Wolfenstein: Enemy Territory, which is a game you need a special program to minimise :D .

(my Windows is in Slovak)

This will terminate all non-responsive programs and allow you to resume normal functionality:

taskkill /f /fi "status eq not responding"

You can run it from command prompt or start menu.