Linux

mysqld_safe --skip-grant-tables --skip-networking &
mysql mysql
mysql> update user set password=password('aaaaaaaa') where user="root" and host="localhost";
mysql> exit
mysqladmin shutdown
/etc/init.d/mysql start
mysql -u root -p

Windows

C:Program FilesMySQLMySQL Server 4.1bin>"C:Program FilesMySQLMySQL Server 4.1binmysqld-nt" --defaults-file="C:Program FilesMySQLMySQL Server 4.1my.ini" -u root --skip-grant-tables
mysql mysql
UPDATE user SET Password = PASSWORD('pH7AmiEw') WHERE User = 'root';
exit;