I can change windows on my Xterm anymore. What happened?
You may have the NumLock key on. In the fvwm window manager which you are using, numlock is treated like a modifier (like ctrl of shift). You focus on a window by clicking on it, but only an unmodified click will do. When the numlock key is on, you are in fact numlock-clicking, and this won’t work for focussing a window.
