No need to be quite so very rudely dismissive of my post, Guest, Ed. (281213).

If you set your Windows-based PC to allow automatic updates it could conceivably be that one of these had affected michaelr's ability to open his docs created in an older version of Word.
My problem with Mac occurred after upgrading (OK, rather than updating) from Snow Leopard to Mountain Lion: "Microsoft Word 2004 is no longer supported": sure I still had the installation disk but it was now of better/only use as a garden bird-scarer.
I don't profess to be anything like as knowledgeable as JohnInKanasas, who regularly provides very helpful advice - and is polite to other posters: I was merely reporting my experience.