Excel keeps asking me to activate and it still won't work

I've been using Office365 for MAC for more than a year.  This morning, when i tried to open Excel, I got a messaging asking me to activate my subscription.  When I put in my e-mail and password, I get a message congratulating me and saying that my Office for Mac is ready to use.  Then when i try to open up a document, I get the same message asking me to Activate.  No matter how many times I activate, I still can't use anything because it keeps asking me to activate!  I have tried deleting all Microsoft files and reinstalling and I still have the same problem.  Curiously, the same subscription on my laptop and on other computers where i have it installed work as always with no problem.  Help!!