I've been back and forth with blogger's tech support for some months now. The Problem? When you set your template to allow you to edit a post while signed in, you should see a little pencil at the end of each post. I couldn't see any pencil. Seeing as they're free, I can't complain about blogger too much, but their "help" consisted of several different ways of saying: "Well, we can see it so it must be something wrong at your end." I wasn't trying to blame anyone; I was merely looking for help. You know, getting it to work again? I had already guessed the problem was here somewhere, but it would have been nice if they had given me a few suggestions.
Anyway, I finally solved the problem. It was the settings on my Norton Internet Security. If any of you are having the same problem, or if you know someone who is, here's what you can try:
Open NIS and go to 'options.' Click on the 'web content' tab and add www.blogger.com to the list of sites. I also added the address for my specific blog, but I don't know if you have to or not. Once the site is added, you can adjust the individual settings for that site using the other tabs. The one that seemed to make the difference for me was permitting the 'information about visited sites,' although I don't know why exactly. But experiment with those and you might have some success.