Often, one of the plugins in WordPress can cause an issue for everything else. This will manifest itself as blank pages, errors or a very slow site. The best way to see if this is the root cause of the issue is to disable all your plugins and see if the issue goes away and enable one by one.
You have a few options
1. Login to the WordPress admin area and then go to Plugins on the left hand side and then Installed Plugins and then click Deactivate on each one.
2. You can access the database using PHPmyadmin or similar and then run this query:
UPDATE wp_options SET option_value = '' WHERE option_name = 'active_plugins';
3. You can also do it via FTP / File Manager. Simply access this on your hosting and then go to /wp-content/ and then rename the plugins folder e.g. disableplugins