Well, I'll give an update on the situation I was having. If you remember me, I was unable to start Kindle for PC on my desktop, but when I downloaded and installed it on my wife's computer it worked fine. Knowing that meant there was something wrong with my computer didn't help because I could not figure out what it was after trying all the suggestions here and at Amazon's forum. So, over the weekend I borrowed my wife's laptop long enough to copy over the AZW files to a flash drive to load them on my computer and run them through calibre to read on my Kobo. Just for the heck of it, after I copied the files to my desktop I double clicked on one of the files and wouldn't you know it, Kindle for PC started right up like it had never had a problem.
Now it wouldn't open the file, gave me an error message and then stated that my installation was not registered to an account. So, off I went to amazon, reregistered my Kindle for PC application to my account, which it now calls My Kindle for PC 2, and it proceeded to download every book I had gotten from Amazon. Several days later, and it still works.
I have no idea if this will help anyone else, but it worked for me.