have you tried:
-deactivating all plugins. If the problem goes away, activate them individually to find the culprit?
If you don't have access to to your admin area, try deactivating them manually via FTP or phpMyAdmin.
-switching to the default theme to rule out any theme-specific issue?
If you don't have access to your admin area, then access your server via FTP or SFTP or whatever file management application your host provides.
- resetting the plugins folder by FTP or phpMyAdmin? Sometimes, an apparently inactive plugin can still cause problems.
-if that does not resolve the issue, try increasing memory available for php.