Hi musterbeispiel,
To login to Office 365, it is recommended that users use the URL https://portal.microsoftonline.com. In addition, because Office 365 account and Windows Live ID are different Microsoft services, users are not able to log into Office 365 via https://login.live.com page.
Since Chrome and Opera are not the product from Microsoft, I suggest trying to log into your Microsoft Office 365 Portal and Outlook Web Apps by using Internet Explorer(IE).
If you still cannot log into your Microsoft Office 365 Portal via Internet Explorer (IE), it will be nice that you can provide the screenshot about the error message. You can post the screenshots here by clicking Use rich formatting, and clicking Insert Image icon.
Thanks,
Maggie Li