login problem to backend as administrator

[stewal]

since a few days it is not possible to log in to the backend of joomla 3.4.5 any more. When I try to log in at the homepage/administrator site with username and password the mask disappears shortly but appears again (empty), but nothing else happens. The password should be correct and there are no error messages shown at all. Just the login doesn't work any more. The same happens for other users and other administrators.
Can anybody help me with this?

[itoctopus]

There are many, many reasons for this problem, including an incorrect log/tmp path in the configuration.php file, disabled ACL extensions, corrupt ACL tables, hacked website, etc...

It's really hard to tell what the issue is without having more context.

[harperlala]

you can set error_reporting to maximum in configuration.php file.

[stewal]

I've set the error reporting in the configurator.php file from default to: public $error_reporting = 'E_ALL';

but when I look into the logs/error.php file the last entry is from two months ago, that's strange (is there another error log file somewhere?)

[stewal]

I think the database is attacked by a foreign computer. There is a continuous query running. I've already sent a message to my provider. Is there a possibility to restart the sql database via the phpMyAdmin interface or a command to stop the query from outside? If I try to kill the running thread it just changes the id number and can't be killed... Any idea what to do ...besides deleting the database