I cannot log in to my WordPress admin.

I don’t know what I did. I copied my user name and password when I first downloaded WordPress. The first time I tried to go to the dashboard, WordPress wouldn’t let me in. It not only wouldn’t recognize any combination of user names or passwords that I would have used, but it would not recognize either of the email addresses that I used. I tried to reinstall WordPress, but I didn’t get anywhere with that. I would appreciate any help.