Sometimes the server can experience glitches and this can cause the CMS to act up. Try refreshing your screen (Reload / F5 on your keyboard) to see if that resolves the issue.
Other times, a blank CMS can be caused by two or more users being logged into the system using the same login credentials. This causes your cookie to break which, in turn, breaks your CMS.
It is crucial that you use your own login credentials to access the system and update your website via the CMS. If you don't have your own, contact us and we'll sort you out.
A blank CMS can also occur when a user uses their own login credentials in two or more browsers, so don't do that either! :)