example.com/wp-login.php "no data received" but example.com works

I cannot connect to example/wp-login.php now.
Story is….I had a problem before that. I could not login.

When I submit account name and password form example.com/wp-login.php, it was redirected to http://example.com/wp-login.php?redirect_to=http://example.com%2Fwp-admin%2F&reauth=1 without showing any message like “wrong password”.

So I was trying to fix it by changing name of directory of plugin, changing theme directory name. Nothing happened.

I commented out the following code in template-loader.php

if ( defined('WP_USE_THEMES') && WP_USE_THEMES )
    do_action('template_redirect');

Then no data received.

I am lost now. Could somebody help me please?

https://ww.wp.xz.cn/plugins/forum-server/