Now I have done a few things: first I installed lubuntu. It worked as if nothing is wrong!! I could have stayed with it, but then I discovered that it supports only one language: I need multiple languages because we all speak different languages. I found out that that one of the feature that LXQt doesn't have but LXDE does, so I tried xubuntu: it worked!!

I still don't know why mint, MX, and ubuntu didn't work. But I'm more or less happy with xubuntu (Except that my konica-minolta bizhub C3100P doesn't get recognized!), so I'm going to leave it as it is. Thanks a million to all, for all your help+advice!