Unfortunately, none of the suggestions worked (or, I am not doing them correctly). I have tried several times to have the password e-mailed to me, but it continues to say that the user doesn't exist--even though it is clearly listed as a user in my phpmyadmin panel from MAMP. Sometimes I do get the message that a password has been e-mailed to me, but then it isn't. In fact, I don't have a single e-mail from WordPress regarding my local setup, so I'm not sure how my email would be registered in the first place.
I have changed my password in phpmyadmin, and the change shows up on MAMP, but then doesn't work when I go and try it. I have tried every possible combination of username, password (root, admin, ADMIN, TheScienceRoom, etc.) and I just keep getting the annoying shaking of the screen that is making me dizzy at this point.
The strange thing is that I have been playing around with my website for weeks, and haven't had to log in at all until recently--which is why I don't have a clue what my username or password might be.
It looks like I'll have to delete every file and start from scratch. Thanks so much for the suggestions, though.