Hello,
I have Office 365. When I try to start power pivot add-in then I see in the bottom right corner "Loading data model..." but power Pivot window will not open. I have tried to reinstall Office 365 https://support.office.com/en-us/article/Manually-uninstall-Office-2016-or-Office-365-4e2904ea-25c8-4544-99ee-17696bb3027b but with fresh installation I got the same error. I tried to follow also these steps https://support.office.com/en-us/article/Start-the-Power-Pivot-in-Microsoft-Excel-add-in-a891a66d-36e3-43fc-81e8-fc4798f39ea8 but again without any luck. Is there a way how to make it work? Thanks