There are times when there is some problem in your plugin that you have installed in your site and your site goes blank. In this situation you will not be able to log in to the WordPress Admin area to manually disable all of the plugin. In this situation you can simply use the database to disable or enable all your wordpress plugins.
Step 1: It is highly recommended to backup your database before your work on any database command.
Step 2: Login to your database using phpMyAdmin (or whatever), Click on your database and click on the SQL tab and enter the following SQL query:
UPDATE wp_options SET option_value = ' ' WHERE option_name = 'active_plugins';
This query will disable all the active plugins.