DBI connect failed : Access denied for user ''@'localhost' to database 'mysql'

Hi Forum,

I've mistakenly changed MYSQL root user name from "root" to "xyz" using COMMAND :

update mysql.user set user='xyz' where user='root'; flush privileges;

But after exiting from MySql when I tried to reopen command prompt of MySql I could not enter using the previous password and whenevr I was trying to use mysql database it was showing : Access denied for user ''@'localhost' to database 'mysql'

I have also tried with changing root password and finally reinstalled the mysql but same thing is happening till now.

Till now using Command :

select user(),current_user(); I am getting user - root@localhost and current_user - ''@localhost

Please help me in that so that I can connect mysql and proceed with my work.

Thanks in advance

Rajhrita