Cannot log in to the MySQL server

I think that you should reset the password of root user.

How to reset MySQL root password.

To reset your mysql password of root user, just follow these instructions.
Step1. Stop the mysql demon process using this command :

sudo service mysql stop

Step2. Start the mysqld demon process using the --skip-grant-tables option with this command:

sudo /usr/sbin/mysqld --skip-grant-tables --skip-networking &

Step3. Start the mysql client process using this command:

mysql -u root

Step4. From the mysql prompt execute this command to be able to change any password:

FLUSH PRIVILEGES;

Step5. Then reset/update your password and quit:

SET PASSWORD FOR root@'localhost' = PASSWORD('password');
quit

Step6. Start the mysql demon process using this command :

sudo service mysql start

Now, you can log in to MySQL as root user.