You need to start MySQL using the defaults-file that the installer wrote for you.
Start | Run "services.msc" (without the quotes).
Find the MySQL service. Right click, Properties
Path to executable will have something like --defaults-file="C:\ProgramData\MySQL\MySQL Server 5.6\my.ini"
So, if MySQL is running, you'll need to stop it. You can do that from the Services snap-in.
Open a Windows command prompt, and run
c:\Program Files\MySQL\MySQL Server 5.6\bin>mysqld --skip-grant-tables --defaults-file="C:\ProgramData\MySQL\MySQL Server 5.6\my.ini"
or whatever your defaults-file is. The command promt will appear to hang. That's because the server is still running. It won't return until you stop the server.
Open another command line. You should then be able to run
C:\>mysql
mysql>USE mysql;
mysql>SELECT * from users;
and see what users have been defined, like PB showed you.
To stop the MySQL server when you are finished, use
C:\>mysqladmin -shutdown
Restart the MySQL service from the Services snap-in.
If you want look at / edit the my.ini file, C:\ProgramData\ is a hidden folder, you'll need to unhide it. (Notice no space in ProgramData).
Good luck,
Barry.