Thank you for your suggestions, although I'm not sure what 'not seeing the problem before', or expressions of doubt in my believability means. I have no reason to make this up, and try not to be a bother on these pages. This problem, however, whatever the cause, is real and is beyond my modest abilities to correct.
I tried all the steps you graciously suggested, but the end result is the same. Each time I reinstall or re-download, (whichever version), MC16 reappears, will not open, and it's icon appears over the icons of numerous other programs (i.e. IE9, my Verizon Wireless modem, Reaper. and others). It tries to open these programs, and can't. My program defaults are all set to their proper places, according to the default manager. (My MC15 version continues to work fine throughout).
I wish I knew how to show you the before and after, but I don't.
For what it's worth, the change occurs while the install wizard is running. The icon appears over the other programs at this point, and installation continues. (I've tried 'custom intallation, and deselecting all file associations on that screen. This doesn't help). When installation is finished, MC refuses to open.
Just so you know, I run windows 7-64 Home on an HP laptop.
Thanks again for your help. This is, however, a holiday weekend, and I surely hope you don't spend it on my problem It can wait till next week.