Possible reason ONE:
You are using the beta version, in which the "Account" button is gray.
Please upgrade to the latest version. Please find the installation package from the group files or our official website.
Possible reason TWO:
You are using the PowerPoint 2007.
Microsoft PowerPoint 2007 doesn't allow you to log in and use the online features. Please upgrade your Office version. Office 2016 or Office 365 is recommended.