Thanks, I have tried this, but it does not make it look any better.
After deactivating iCloud, the computer was asking for one infinitely many passwords to use the "login" keychain (popups coming as soon as I entered the password of the previous one, with apps I entered the password to coming up again). The machine is essentially unusable now. That much closer to the clean re-install. Upon closer inspection, it seems that reactivating the iCloud keychain does not seem to do anything... More interestingly, my "login" keychain password seems synchronised with my OLD iCloud account password.
Very frustrating ! What a stupid piece of garbage Keychain is, I cannot believe it.
[doublepost=1487344442][/doublepost]As a last resort attempt, I am changing all my passwords (login and iCloud) to the same thing. I just cannot understand why the "login" keychain inherited some old iCloud account asking for it (and also, it is a password I do not use anymore ----it is quite fortunate I remembered it and had the idea to try it out).