What happenes when you try and do a password reset? Does it say the user does not exist?
The only thing I can really suggest, is to access phpmyadmin through your webhost.
From there you can access the wp_users table and update the username and password through there. You'll need to MD5 hash the password before storing back in PHPmyadmin tho.
I would have a read through here. I wrote that blog posts for users who need help resetting the password via phpmyadmin.
If all else fails and your not comfortable I would reach out to your host and let them know your having trouble. I'm sure they can reset the password for you.