Auto backup files (ending with ~) stopped working. Why? Options

[linuxlover992000]

I appologize up front for the double-post (I mistakenly posted this
request for help in the wrong newsgroup a few minutes ago):

I was happily editing some text files using emacs  when I suddenly
noticed that it does not automatically create the famous ~ backup
files for them.

I swear that I did not touch .emacs anytime recently. Yet, the sudden
disappearance of this useful feature occured only last night.


What could be the possible explanation(s) for such strange behavior?
Is it possible that I mistakenly hit some key combination that turned
off that feature forever? If so, how do I restore it?


Any idea?


Thanks,
Lynn