Govpatel’s advice is always good. If that doesn’t sort it out for you also try the usual troubleshooting steps.
Have you tried:
– 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).
– switching to the Twenty Eleven theme to rule out any theme-specific problems.
– resetting the plugins folder by FTP or PhpMyAdmin. Sometimes, an apparently inactive plugin can still cause problems.
– re-uploading the wp-admin and wp-includes folders from a fresh download of WordPress.
Also consider giving this a good read too.
https://www.ads-software.com/support/topic/troubleshooting-wordpress-34-master-list?replies=4