My WordPress Site Stopped Working!
The vast majority of sudden WordPress meltdowns are due to plugin conflicts. This is especially true whenever you upgrade a plugin or WordPress itself.
If this happens to you, try deactivating all of your plugins and check to see if this resolves the problem. If it does, activate the plugins one by one – checking your site after each re-activation – until you find the problematic plugin(s).
If the problems are so bad that you can’t even login to your blog, use FTP to access your wp-content/plugins folder and rename each of the individual plugin folders. Do the same for any scripts in the plugins folder. This will automatically deactivate all plugins and, hopefully, allow login access.

Scrapbook 5.2 - Russian translation