Please access to the SharePoint Online with your Office 365 account to check whether it shows a blank window. Meanwhile, please let other users in your organization try accessing the SharePoint follow the way you mentioned above on your Outlook client to confirm whether this issue also occurs with his Office 365 account.
Moreover, please clear the cache of your IE browser with the steps below and check if the issue can be fixed.
1. Please go to IE settings > General > Settings under Browsing history > Caches and databases.
2. Delete cache files for the website "outlookapps.com".