Hi Alex,
I understand how it feels when you are unable to work with the application as the popup keeps appearing on the screen. Let me assist you with the issue.
What happens when you put in the credentials and click OK, are you able to use PowerPoint normally?
You may sign Out of Office and check if the issue occurs.
If the issue persists, you may remove the stored credentials following these steps and then re-login and check if the issue occurs:
- Open User Accounts by clicking the
Start button , go to Control Panel, click
User Accounts and Family Safety (or click User Accounts, if you are connected to a network domain), and then clicking
User Accounts.
- In the left pane, click Manage your credentials.
- Click the vault that contains the Live account credential.
- Click the credential, and then click Remove from vault.
Now sign-in to Office again and check if the issue occurs.
Let us know if you need further assistance.
Thank you.