service mysql restart --skip-grant-tables --skip-networking

[mysqld]
skip-grant-tables
skip-networking

net stop mysql (wait 10 seconds)
net start mysql

INSERT INTO mysql.user SET
Host='localhost',
User='mynewuser',
Password=PASSWORD('whateverpassword'),
Select_priv='Y',
Insert_priv='Y',
Update_priv='Y',
Delete_priv='Y',
Create_priv='Y',
Drop_priv='Y',
Reload_priv='Y',
Shutdown_priv='Y',
Process_priv='Y',
File_priv='Y',
Grant_priv='Y',
References_priv='Y',
Index_priv='Y',
Alter_priv='Y',
Show_db_priv='Y',
Super_priv='Y',
Create_tmp_table_priv='Y',
Lock_tables_priv='Y',
Execute_priv='Y',
Repl_slave_priv='Y',
Repl_client_priv='Y';

service mysql restart

select user,host,password from mysql.user;

DELETE FROM mysql.user WHERE ...;
FLUSH PRIVILEGES;

desc mysql.user;

SELECT CONCAT('SET ... ',GROUP_CONCAT(CONCAT(column_name,'=''Y'''),';'))
FROM information_schema.columns
WHERE table_schema='mysql'
AND table_name='user'
AND column_type='enum(''N'',''Y'')'
ORDER BY ORDINAL_POSITIONG