I’m was having exactly the same problem. Research via Google said the likely problem was a plugin, so to fix it, I loggged into my server directly, went to the wp-content/plugins directory, made a new directory called “Disabled”, and moved all my plugins into it, then restarted the httpd service.
The expected login screen came right up, and I was able to log in. Of course, when I go to the “Plugins” management tab, there’s a pile of errors because it can’t find any of the plugins, so I’m putting them back one at a time and checking to make sure it’s still working. That’s going to take a while, but since I was already here, I thought I’d share what I found that worked.
This is unusual — it was working fine last week, and this week, not. Without me making any changes, applying updates, etc. I wonder what changed?