on various sites that are running very well i cannot log in

Try manually resetting your plugins (no Dashboard access required). If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, access your server via SFTP or FTP, or a file manager in your hosting account’s control panel, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the default theme to activate and hopefully rule-out a theme-specific issue (theme functions can interfere like plugins).

If you can install plugins, install Health Check. On the troubleshooting tab, you can click the button to disable all plugins and change the theme for you, while you’re still logged in, without affecting normal visitors to your site.

Also, it wouldn’t hurt to discuss with your hosting provider in case they have implemented some security measures causing this issue.

• This reply was modified 6 years, 11 months ago by t-p.

hello dear T-P

many many thanks for the hints: great – i will do all you advice!!!
i cannnot login in my sites that run the newest version of wp –

three sites only present a blank page,,,

very interesting: all runs in vhost on a root-server.

i have the issues on three sites on the server:

i activated an older site – which was closed – running WordPress 4.7.8 – with the theme: “Twenty Seventeen theme”with this all works nice – and i can access the login.

In order to get more infos about what is happening i need to see the php-error-logs

to see this i have to change the wp-config.php file and add this too config.php

define(‘WP_HOME’,’localhost/wordpress’);
define(‘WP_SITEURL’,’localhost/wordpress’);

Then i need to restart the apache and i hope i could enter again on my admin panel. ..But everytime i u use the …/wordpress/wp-login.php i receive a 404 not found

see the sessions: #

Session Support enabled
Registered save handlers files user mm
Registered serializer handlers php_serialize php php_binary
Directive Local Value Master Value
session.auto_start Off Off
session.cache_expire 180 180
session.cache_limiter nocache nocache
session.cookie_domain no value no value
session.cookie_httponly Off Off
session.cookie_lifetime 3600 3600
session.cookie_path / /
session.cookie_secure Off Off
session.entropy_file /dev/urandom /dev/urandom
session.entropy_length 32 32
session.gc_divisor 1000 1000
session.gc_maxlifetime 3600 3600
session.gc_probability 1 1
session.hash_bits_per_character 5 5
session.hash_function 0 0
session.name PHPSESSID PHPSESSID
session.referer_check no value no value
session.save_handler mm mm
session.save_path no value no value
session.serialize_handler php php
session.upload_progress.cleanup On On
session.upload_progress.enabled On On
session.upload_progress.freq 1% 1%
session.upload_progress.min_freq 1 1
session.upload_progress.name PHP_SESSION_UPLOAD_PROGRESS PHP_SESSION_UPLOAD_PROGRESS
session.upload_progress.prefix upload_progress_ upload_progress_
session.use_cookies On On
session.use_only_cookies On On
session.use_strict_mode Off Off
session.use_trans_sid 0 0

what seems to be vers interesting is this line.

session.save_handler mm mm

t-p. now i will follow all your advices..

many many thanks so far.
i come back and report the findings.