This isn't my area of expertise—I'm more a programmer, not an installer or systems guy—but if I were having this trouble, I'd either try to find someone at Microsoft to help, or, having pre-given up on that in disgust, just remove and reinstall. Sorry, I don't have any other ideas.

In this pessimistic mood I'm partly affected by the observation that there are a small number of things I used to do in Office that no longer work the same. In some cases I'm convinced they moved or upgraded the capability but neglected to document it where I can find it; in two or three, it doesn't seem to act as it should and I suspect, from my own experiments and from reading on the web, that it's a bug they still haven't fixed since it was reported in 2011. From that and the fact that the standard of documentation has gone downhill too—important data missing from the references, and even when I try to add them myself I'm told, invariably but uninformatively, "there was a problem when we tried to add your comment"—I begin to wonder whether Excel, Outlook etc have simply gotten too complex to maintain any longer; maybe some new basement hobbyist will now come along and eat their lunch, amidst chaos and disorder for the next few years.

But I tend to get these grouchy phases when I'm having trouble making things work right, and the fact that my decades-old ISP (AT&T) is increasingly unable to deliver email, as well, is adding to the mood. Maybe in another few months I'll have dug to the bottom of all these problems and will be back to my usual sunny assumptions about the magnificence of everything around me.