How can I understand what is the cause of WP death (white screen)?

Question

I have some problems on a admin side:
when i try to filter posts according to any category, or when I publish a post, I see a white screen of WP death...
The content of debug.log is:

    [17-Jun-2012 11:49:55 UTC] PHP Warning:  include(/home/dinorg/public_html/wp-content/advanced-cache.php) [<a href='function.include'>function.include</a>]: failed to open stream: No such file or directory in /home/dinorg/public_html/wp-settings.php on line 62
    [17-Jun-2012 11:49:55 UTC] PHP Warning:  include() [<a href='function.include'>function.include</a>]: Failed opening '/home/dinorg/public_html/wp-content/advanced-cache.php' for inclusion (include_path='.:/usr/lib/php:/usr/local/lib/php') in /home/dinorg/public_html/wp-settings.php on line 62
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  Constant BLOGUPLOADDIR already defined in /home/dinorg/public_html/wp-includes/ms-default-constants.php on line 28
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  wp_enqueue_script נקרא <strong>בצורה לא תקינה</strong>. סקריפטים וסגנונות לא צריכים להרשם או להיטען לפני ווים <code>wp_enqueue_scripts</code>,<code>admin_enqueue_scripts</code>, או <code>init</code>. כנסו ל-<a href="http://codex.wordpress.org/Debugging_in_WordPress">Debugging in WordPress</a> למידע נוסך. (הודעה זו נוספה בגרסה 3.3.) in /home/dinorg/public_html/wp-includes/functions.php on line 3587
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  define() was called with an argument that is <strong>deprecated</strong> since version 3.0. The constant <code>VHOST</code> <strong>is deprecated</strong>. Use the boolean constant <code>SUBDOMAIN_INSTALL</code> in wp-config.php to enable a subdomain configuration. Use is_subdomain_install() to check whether a subdomain configuration is enabled in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Notice:  has_cap was called with an argument that is <strong>deprecated</strong> since version 2.0. Usage of user levels by plugins and themes is deprecated. Use roles and capabilities instead. in /home/dinorg/public_html/wp-includes/functions.php on line 3551
    [17-Jun-2012 11:49:55 UTC] PHP Warning:  Cannot modify header information - headers already sent by (output started at /home/dinorg/public_html/wp-content/themes/din/admin/qa_db.php:1) in /home/dinorg/public_html/wp-includes/pluggable.php on line 866

It is reasonable that the last row (Cannot modify header information - headers already sent) points to the critical problemm, however it's unclear for me, what does it mean. And is it realy the critical problem?
Thank you for any help with it!

Answer 1

In your /home/dinorg/public_html/wp-content/themes/din/admin/qa_db.php something wrong. It is unusual that first line of a script will print something unless you opened php tag (or php shorttag) and put some codes in same line. So i guess that file may have something like BOM. Please open the file and see if you notice any weird characters.

if you are on server (terminal), you can use the file using vi (or vim).or you can open it using a file browser, if you have any control panel (like cpanel, plesk etc.). you can also download the file and upload to a file sharing site and attach the link in the comment so that we can see if the file has something wrong (if the file is publicly shareable).

to get error details rather than dead white page, please put the following in the /home/dinorg/public_html/wp-config.php.

ini_set('display_errors', true) ;
define('WP_DEBUG', true);

please let us know the outcomes.