Easy steps to reset mySQL root password:

1. Check the version of mysql-server;

   apt-cache policy mysql-server
   

   and you will see string like this:

   Installed: 5.5.26-0ubuntu0.12.04
   

   it means that you have a mysql-server-5.5 installed in your system

2. Start reconfiguration:

   sudo dpkg-reconfigure mysql-server-5.5 < version of mysql server
   

3. Change the password on this screen:

1. Try connect:

   mysql -u root -p
   

You can read full answer by this link.