i had the same problem. I tried to insert a new username and password and it never worked. You aren't obliged to insert a username and password before you can view and edit your databases from mysql( That was what happen to me, i dunno if your's the same, i could access my databases directly). U can directly access your databases, try to type
and then, to use a database, type
If you feel not secure, or working on another guy's pc, i would suggest you to put a username and password.
Hope i helped you