wordpress admin problem/stopped working

Hello,

My wordpress admin has suddenly stopped working. mysite.com/wp-admin redirects to http://beam.pk/wp-login.php?redirect_to=http%3A%2F%2Fbeam.pk%2Fwp-admin%2F&reauth=1 and after putting in login credentials it gives a 404 error page.

Here are few things I have done:

Cleared cache/cookies etc
Checked .htaccess for any code that may be causing the redirect but found none. Its pretty default.
Renamed the plugin folder and it takes me to the dashboard but can’t do anything from there. It gets stuck there and leads to a 404 eventually.

Below is my error log report. Another thing is when I change the wp_debug to true, all my sub page i.e. posts etc. show a blank page and when I turn it off, everything turns normal. Anyway below is my error log report:

[06-May-2016 09:34:01 UTC] PHP Warning: include_once(/home/beampk/public_html/wp-content/plugins/wordpress-seo/wp-seo.php): failed to open stream: No such file or directory in /home/beampk/public_html/wp-settings.php on line 255
[06-May-2016 09:34:01 UTC] PHP Warning: include_once(): Failed opening ‘/home/beampk/public_html/wp-content/plugins/wordpress-seo/wp-seo.php’ for inclusion (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/beampk/public_html/wp-settings.php on line 255
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[06-May-2016 09:34:01 UTC] PHP Warning: strpos(): Empty needle in /home/beampk/public_html/wp-includes/plugin.php on line 679
[08-May-2016 20:47:34 Europe/Moscow] PHP Fatal error: Call to undefined function wp() in /home/beampk/public_html/wp-blog-header.php on line 16
[08-May-2016 20:49:10 Europe/Moscow] PHP Fatal error: Call to undefined function wp() in /home/beampk/public_html/wp-blog-header.php on line 16
[08-May-2016 20:56:45 Europe/Moscow] PHP Fatal error: Call to undefined function wp() in /home/beampk/public_html/wp-blog-header.php on line 16
[08-May-2016 20:56:45 Europe/Moscow] PHP Fatal error: Call to undefined function wp() in /home/beampk/public_html/wp-blog-header.php on line 16
[08-May-2016 20:56:45 Europe/Moscow] PHP Fatal error: Call to undefined function wp() in /home/beampk/public_html/wp-blog-header.php on line 16

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Any help in this regard will be highly appreciated.

Thank you