Windows下mysql忘记root密码的解决方法：
Mysql版本：5.1.55-community MySQL Community Server (GPL)
1、 首先检查mysql服务是否启动，若已启动则先将其停止服务，可在开始菜单的运行，使用命令：
net stop mysql
或者在windows任务管理器中结束mysqld.exe进程，或者在控制面板，管理工具里面的服务找到mysql，将其停止服务。
打开第一个cmd窗口，切换到mysql的bin目录，运行命令：
mysqld --defaults-file="C:\Program Files\MySQL\MySQL Server 5.1\my.ini" --console --skip-grant-tables
注释：
该命令通过跳过权限安全检查，开启mysql服务，这样连接mysql时，可以不用输入用户密码。
"C:\Program Files\MySQL\MySQL Server 5.1\my.ini"指配置文件my.ini，一般在mysql安装目录里面。
如：
===============================================================================
C:\Program Files\MySQL\MySQL Server 5.1\bin>mysqld --defaults-file="C:\Program Files\MySQL\MySQL Server 5.1\my.ini" --console --skip-grant-tables
110301 9:20:07 [Warning] '--default-character-set' is deprecated and will be removed in a future release. Please use '--character-set-server' instead.
110301 9:20:07 [Note] Plugin 'FEDERATED' is disabled.
110301 9:20:07 InnoDB: Initializing buffer pool, size = 46.0M
110301 9:20:07 InnoDB: Completed initialization of buffer pool
110301 9:20:07 InnoDB: Started; log sequence number 0 44233
110301 9:20:07 [Note] mysqld: ready for connections.
Version: '5.1.55-community' socket: '' port: 3306 MySQL Community Server (GPL)
2、打开第二个cmd窗口，连接mysql：
输入命令：
mysql -uroot -p
出现：
Enter password:
在这里直接回车，不用输入密码。
然后就就会出现登录成功的信息，
如：
===============================================================================
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 3
Server version: 5.1.55-community MySQL Community Server (GPL)
Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
===============================================================================
使用命令：
show databases;
显示已有数据库：
+--------------------+
| Database |
+--------------------+
| information_schema |
| mysql |
| test |
+--------------------+
3 rows in set (0.00 sec)
使用命令切换到mysql数据库：
use mysql;
使用命令更改root密码：
UPDATE user SET Password=PASSWORD('newpassword') where USER='root';
刷新权限：
FLUSH PRIVILEGES;
然后退出，重新登录：
quit
重新登录：
mysql -uroot -p
出现输入密码提示，输入新的密码即可登录：
Enter password: ***********
显示登录信息：
Welcome to the MySQL monitor. Commands end with ; or \g.
Your MySQL connection id is 9
Server version: 5.1.55-community MySQL Community Server (GPL)
Copyright (c) 2000, 2010, Oracle and/or its affiliates. All rights reserved.
This software comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to modify and redistribute it under the GPL v2 license
Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.
mysql>
到这里root密码就已经修改成功了，用Ctrl+C将第一个cmd窗口结束，那样就会停止mysql服务，如：
=============================================================================== C:\Program Files\MySQL\MySQL Server 5.1\bin>mysqld --defaults-file="C:\Program F
iles\MySQL\MySQL Server 5.1\my.ini" --console --skip-grant-tables
110301 10:29:47 [Warning] '--default-character-set' is deprecated and will be re
moved in a future release. Please use '--character-set-server' instead.
110301 10:29:47 [Note] Plugin 'FEDERATED' is disabled.
110301 10:29:47 InnoDB: Initializing buffer pool, size = 46.0M
110301 10:29:47 InnoDB: Completed initialization of buffer pool
110301 10:29:48 InnoDB: Started; log sequence number 0 44233
110301 10:29:48 [Note] mysqld: ready for connections.
Version: '5.1.55-community' socket: '' port: 3306 MySQL Community Server (GPL)
（此处输入ctrl+c）
110301 10:30:58 [Note] mysqld: Normal shutdown
110301 10:30:58 InnoDB: Starting shutdown...
110301 10:31:03 InnoDB: Shutdown completed; log sequence number 0 44233
110301 10:31:03 [Note] mysqld: Shutdown complete
Mysql服务停止了，输入命令：
net start mysql，即可重新启动mysql服务，如：
===============================================================================
C:\Program Files\MySQL\MySQL Server 5.1\bin>net start mysql
MySQL 服务正在启动 .
MySQL 服务已经启动成功。
C:\Program Files\MySQL\MySQL Server 5.1\bin>