An inability to log out is indicative of a cookie issue. To clear your cookies please find the entry below for your browser and copy the setting selections. If you would like to suggest a browser to be included in this guide please comment below
Firefox: Menu (top right) > History > Clear Recent History and set "Time Range" to "Everything"
Chrome: Menu (top right) > More tools > Clear browsing data
Internet Explorer 11:Tools > Internet Options > (Browsing History) Delete