WordPress Codex has some useful info on how to “How to deactivate all plugins when not able to access the administrative menus?”
One of two methods are available to deactivate all plugins.
Use phpMyAdmin
In the table wp_options, under the option_name column (field) find the active_plugins row
Change the option_value field to: a:0:{}
or
Create an empty plugins folder
Via FTP or your host’s control panel, navigate to the wp-contents folder (directory)
Via FTP or your host’s control panel, rename the folder “plugins” to “plugins.hold”
Via FTP or your host’s control panel, create new folder called “plugins”
Login to your WordPress administration menus
Via FTP or your host’s control panel, delete the empty “plugins” you previous created
Via FTP or your host’s control panel, rename “plugins.hold” back to “plugins”