The login for the Office 365 service requires the user to enter their complete email address as the username.  So the recommended process would be:
1. Go to https://portal.office.com
2. Enter your email address as the username (ie. myaddress@stevenson.edu )
3. When prompted, select Work or Business account
4. Enter your Single Sign On password
5. Click the Sign In button

The Office 365 service licensed to Stevenson faculty, students, and staff is set up to integrate with your Single Sign-On account.  As long as you have an active Single Sign-On account and can successfully access other Stevenson services, the account will work with Office 365.

If you had created another personal Office 365 account after receiving a new computer and used your Stevenson email address to register the personal account, then you need to be sure you click the correct option in Step #3 above.