Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
The first thing to try in such a case is, to click on
Use Another Account
and then enter the same credentials you use, to log in to MS Office with the older email address originally used to register your Microsoft Account. Or, whatever other login works.
Another thing to try is, to Activate your software. (This depends upon exactly what version of MS Office or MS Word you are using - and there are many versions. It may not apply to your version, I am aware... and please let me know what version of MS Office or MS Word etc. you are using.)
Also check that your license to use MS Office (or other similar software suite) has not expired. That might suddenly cause this problem.
Let me know (by using the Reply To Expert function) what happens, what software you have, and what you find out, please. I want to help with this problem.