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Had a happy install of Xfce4 on Mint13 Maya when a power failure has resulted in the every window loosing the min-max-close buttons and the Windows Manager & Windows Manager Tweaks icons being unresponsive. I tried reinstalling some Xfce windows management bits I guessed at in Synaptic Package Manager to know affect. I think I then tried to add KDE windows manager via Synaptic and now when I restart normally it starts into just a black screen with mouse pointer and nothing else. [I have since read I should have earlier tried xfwm4 --sm-client-disable but we are passed that working now]. What next?
The first issue you had because of the power failure was a corrupted session. You could have solved it with
rm -rf ~/.cache/sessions
This doesn't happen to everyone but it seems it happens to people that use gedit (and maybe the mate equivalent) in Xfce.
Actually since you had lost xfwm4 you probably should run