If you have not upgraded your WordPress for quite some time and are still using an old version you might face this problem.
The front end will function as usual, but the admin after logging in will only show the left menu panel. The right section will be completely blank.
Via FTP or File Manage download and / or edit the following file –
Search for the following –
Replace this with
Save and / or upload the file.
That should solve the problem.
Also never ignore to upgrade WordPress to the latest version. It will keep your site safe from security and other threats.