Ahh, a happy ending. I called upon my very computer proficient wife to help. She first tried logging in on her Firefox using my username and password. It worked fine.
She cleared the cookies on my machine once more. When she attempted to login, the usual saved form information came up (when I type an M, my whole username comes up and I click on it to fill in the box). She did the same as I would usually do. No login.
Then she tried again, and simply typed in my whole username. Lo and behold, I was logged in. Somehow, the saved information username became contaminated, I have no idea how, it looked exactly the same, namely correct, but it was flawed.
Man, I was ready to pull my hair out, if I had any. I am so relieved. Thanks so very much to Muhammad, Mike PA, JerryG and dholly. Especially Muhammad, who replied to me several times about this problem.
Mike