I installed MySQL using mysql-installer-5.5.20.0.msi on Windows 7. From the cmd window, I run \"mysqlshow -u root -p\". It asked for a password, then return
this issue is very to solve by windows server users
go to this path C:\Program Files\MySQL\MySQL Server 5.1\bin
run this tool "MySQLInstanceConfig.exe"
and config the instatnce again and problem solved