Need Translation Please

Today 3 of my 20 sites decided not to work. (Actually, they all 3 will eventually load after about 3-4 minutes. My other 17 sites load just fine.) Two of them are sub-domains of the first. All 3 are exhibiting this error message in their error.log files:

[17-Dec-2011 17:27:02] WordPress database error MySQL server has gone away for query SELECT t.*, tt.* FROM wp_terms AS t INNER JOIN wp_term_taxonomy AS tt ON t.term_id = tt.term_id WHERE tt.taxonomy IN (‘category’) ORDER BY t.name ASC made by require, require_once, include, include, wp_list_categories, get_categories, get_terms

And the error log in the root of public_html, where all of my sites are loaded, shows this error message(s):

[17-Dec-2011 11:44:51] PHP Warning: require(./wp-blog-header.php) [function.require]: failed to open stream: No such file or directory in /home/pcrum/public_html/index.php on line 17
[17-Dec-2011 11:44:51] PHP Fatal error: require() [function.require]: Failed opening required ‘./wp-blog-header.php’ (include_path=’.:/usr/lib/php:/usr/local/lib/php’) in /home/pcrum/public_html/index.php on line 17

I get that it’s a db problem but exactly what and how do I fix it?

UPDATE: Disregard, please. Turned out to be a problem related to the them I’m using, (Socrates). Their server is being attacked and that’s causing loading problems. whatever the prison term is for this kind of stuff, it’s not long enough.