Password issue - iMac not waking up or stopping screensaver

Hello,

My iMac has been acting weird for a while now, and I think I have finally spotted where the issue is coming from.

It's a password issue:

- I can't unlock the padlocks in system preferences nor can I in keychain. When I click on them, the dialog box doesn't come and the locks go from "authenticating" back to "click to make changes" within 5 seconds.

- When the computer goes into sleep mode, I can't wake it up. When I click on the keyboard or on the mouse, the computer makes the normal sound and the screen turns on, but instead of asking me for my PW, it goes back to sleep within 5 seconds.

- When the screen saver turns on, I can't turn it off. When I click on the keyboard or on the mouse, the screen saver stops, but instead of asking me for my PW, it goes back to screen saver mode within 5 seconds.

Also, I've discovered that this issue is somehow messing up with Time Machine. It simply won't backup. I've already posted 2 threads about the TM issue, still unresolved.

However, someone recommended that I download Onyx. When I installed it, my iMac asked me for my admin PW, and it worked. I immediately checked if I could unlock the padlocks in system prefs, and it worked as well. Then I checked Time Machine, and I could perform a full backup. It was like if my computer had remembered how to ask me for that PW, and that unblocked all the restrictions.

To be clear, at this point I hadn't ran the software yet, I had just installed it.

It's as if downloading and installing a software had forced the Mac to ask me for that PW, which fixed all the rest. Nevertheless, after everything was done, I rebooted and the problem came back.

Any help or advice would be much appreciated.

Thank you.