I can't switch from one window to another

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http://askubuntu.com – Hello fine Gentlemen, i have the following problem and i primarily want to have a way how to analyse this. My problem is that somehow Ubuntu keeps locking me in a certain window/editor. i can then not switch to another one using the mouse or Keyboard. I can however close the window, giving the focus to another window. i can: Move the cursor within the window that contains the focus write in the window that has the focus Click in window that has the focus Click on another window, wait some time and it will switch to the new window. i can't: switch to another window at my convenienc (HowTos)