Site performance, Server errors, outages and tunings

Have you tried to purge all cookies?

[Like Ra]

Have you tried to purge all cookies?

Many times. And changing cookie domain, and changing cookie paths (also separately for the users and the admin)...

When you say that you can’t log in, do you see the log-in screen or can you get that far.
Second question:
If you do see the log-in screen, can you enter your password?
And last question would be: does the screen goes blank or does it do nothing except sit there displaying the log-in screen?

[Like Ra]

It's one of the typical WordPress issues, when you enter the credentials, the password is correct, but the page returns back to the login prompt. There are dozens of possible reasons. And I checked pretty much everything what is known. Including going back to the default theme, disabling all plugins, reboots in between, etc. And yes, different browsers.

Ok, then it loops back to the log-in screen.
You lost or deleted a link.
And you say you checked everything YOU can think of.
What about the links you haven’t checked?

[Like Ra]

No links involved, only one file wp-login.php. The cookies are not getting set, so it loops back.

If the cookies are not getting set, then a subroutine got set wrong or the cookie is being cleared, indicating that the log-in never happen.

Reload the wp-login.php and run a trace routine.
That should tell you where the cookie got place.
I’ll bet that the cookie is set, but it set in the wrong section, so the routing will never see it.
Sort of like setting your car keys down in a place that you never did before and nor remembering where you set then.

[Like Ra]

indicating that the log-in never happen.

This is exactly what happens.

Get it fixed yet ?