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Hi. My name is***** you for your question and the opportunity to assist.
By "stopped working" do you mean the program is telling you that it needs to be activated?
Please sign in to your Microsoft account here: https://account.live.com
From the horizontal menu at the top click Services & Subscriptions and you will see the
information for your Office 365 account.
It's likely this is a payment issue. From the menu at the top click Payment & Billing>>Payment Options
Click Add a Payment Method in blue.
Once that has been set up remove the old card information.
To re-install Office 365 go here: www.office.com/myaccount
Click Install on the left side of the page then on the new page
click Install again on the right hand side.
Let me know the result please.