Windows 10: Files from previous MS365 Office are not recognized in recently installed MS365 Office

I just installed MS365 Office after my old subscription had expired in December. It was not on auto-renewal. My old Windows 10 was then interfering with my ability to modify my files so a computer help service at a major store said that before I could use the new Office they had to uninstall Windows 10. Which they did. However after that, some files I had made, using my previous Office, did not associate with the recently installed MS365 Office e.g. Excel, PPT, and nowI can't open them. I can only open them with open-source office-type software e.g. Neat Office or Trio Office.And yes, I h

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MS365 error message

MS365 is the online service previously know as Office 365. If you have either installed a trial version or the full version of Office 365, you might need to uninstall the Office 365 software.

 

MS365 error message

I donot have a MS365 subscription, but keep on getting pop-ups that my subscription has expired. How do I fix this?

 

MS365 subscription valid, but programs say 'unlicensed'

Have MS365 on this laptop, my desktop & wife's desktop. I maintain an Access database of my Club's membership; actual file on USB drive for portability. I have kept my Office version up to date all along. At each meeting I generally have to add new membership records and/or update older records. At the last monthly meeting, I could open MS365 files but not edit them (on this same laptop; had been routinely updating/editing records at monthly Club meetings for several years). For Word, Excel & Access I got a warning of an unlicensed product in title bar of each. When I got home, everything was fine (on laptop & desktop both); I could open and edit files in all three Office programs. What gives? My MS365 subscription is active & up to date. Note: Win 8.1 on my desktop, Win 10 on this laptop & wife's desktop.