Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hi Out Vakantiehuizen,
Based on the description, I understand that you are trying to sign in Office 365 mailbox via using Outlook Web App. If so, may I know which internet browser are you using? Please provide us with the detailed information about this.
Please try to clear/reset the browser cache to check this issue.
Have you tried to check this issue via using different browsers? If not, please try to check this issue via using InPrivate browsing session with latest version of Edge, Internet Explorer and Incognito Chrome session to see whether it is specific browser side issue.
When you say “Only on 1 pc with Windows 10”, I would like to confirm whether using different PC with the same Office 365 user account working correctly without any issue.
Best regards,
Shyamal