ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

ERROR 1045 (28000): Access denied for user 'root'@'localhost' (using password: NO)

>>disabling password authentication
service mysql stop

wait until MySQL shuts down. Then run

mysqld_safe --skip-grant-tables &

then you will be able to login as root with no password.

mysql -uroot mysql

In MySQL command line prompt issue the following command:
use databasename;

UPDATE user SET password=PASSWORD("abcd") WHERE user="root";
FLUSH PRIVILEGES;
EXIT

/etc/init.d/mysqld restart

At this time your root password is reset to "abcd" and MySQL will now
know the privileges and you'll be able to login with your new password:

mysql -uroot -p mysql

(Source: LinuxDeal)