I've been using MX Linux from about 6 months. Firstly, I've installed MX-14 to my cashier computers and it ran well. But suddenly, one of them lost it's window options (minimize, maximize, and close window). Whenever I wanted to close a window, I had to find the close, quit, exit, or such option in it's menu bar. Plus, I couldn't move the window, so the windows got stuck in the position where they have opened. It was like the menu bar of any programs were not functioning at all.
Another system got it's desktop locked. All shortcuts on my desktop were gone, I couldn't even click the desktop (both left and right click were not functioned in the desktop), so I needed to open the start menu to change my desktop background image and put my application launcher to the panel.
I thought that that was a bug in the system, so I've tried to install MX-15. The same problems happened again -_- So does the same with the MX-16.
I don't know what have caused those problems and how to solve them, plus how to prevent them to not be happened again in the future.
Note that those problems happened repeatedly in a lot of computers, even after I have re-installed the system.
I am a newbie, so correct me for any mistakes, plus forgive me for any English errors.

Wow, that is a new one. Its like your window manager isn't running. xfce using xfwm4 as its window manager. you could check to see if that's running.

at first guess, I would say that something has run afoul and the "save session" setting has saved the changes. You could try clearing the saved sessions, which I think you can do in "Session and Startup". then logout and login.

the same probably holds true of the desktop icons. that is controled by xfdesktop. and certain non-xfce filemanagers (like nemo and caja) have been known to take over the desktop if you even just install and run them once.

I'll try them tomorrow and post the results here. Actually, I'm still not sure what to do with xfwm4 and xfdesktop

they should show up as entries in "session and startup".