Hannah’s suggestions is good and does not take long to do, so its a good step. If it fixes the problem, reactivate the plugins one-by-one to try to identify which one is causing the conflict.
You might also temporarily switch to the default TwentyFourteen theme to be able to rule out a theme issue.
If the problem persists when you have deactivated all plugins and tried another theme, it looks like your WordPress install is not complete or corrupted. You have reported 2 things that are missing. Consider a manual reinstall of WordPress.
Download a fresh copy of WordPress and unpack it on your hard drive. Using FTP or your host’s file manager software, copy the files to your webserver. Be careful not to overwrite wp-config.php or your wp-content directory. Take a backup and read the instructions before starting.