follow this instructions see that brings your website back.
1. deleting/renaming your .htaccess. it’s possible that a .htaccess rule could be the source of the problem.
2. deactivating all plugins to see if this resolves the problem? If this works, re-activate the plugins one by one until you find the problematic plugin(s).
If you can not log in admin panel then using ftp rename plugins folder and create a blank plugins folder and try to go on website.
If you can log in fine then go back and delete the blank plugin and rename your original plugin folder back to plugins.
and then refresh admin and deactivate all plugins and activate one at time to find the one causing problem.
Deact
3. switching to the default theme to rule out any theme-specific problems? If you don’t have access to your admin panel, access your server via FTP or SFTP, navigate to /wp-content/themes/ and rename the directory of your currently active theme. This will force the Default theme (Twenty Ten theme) to activate and hopefully rule-out a theme-specific issue
4. resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
5. re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress?
