Try this on the localhost database (not the live site!):
First get the id of your admin user record on the mdl_user table:
SELECT id, username, auth
WHERE (username = 'your_username')
That will show you the admin user record. Take the value that it shows in the id column and use it to change the authentication type for this admin user to manual:
SET auth = 'manual'
WHERE id = 1
AND username = 'your_username';
I'm assuming that your admin id = 1. You need to change it to the correct value that you got from the first query above.