Use the controller layout key below to do the code:
x[2][4] [Turn]
[1][3][5] [ 1 ]xxxx[Start]..
Insert your credits and then Hold [1] and [4] and then Turn 1 Clockwise once. Now Hold [2] and [5] and then Turn 1 Clockwise once. Finally, Hold [4] and press [Start], then Release [4] and Press [2]. If you did it right, you should be able to select all songs.
During the DJ Battle, if you hit one of the five keys on your side, it'll change the sound of the scratch your turntable makes. It doesnt add to the overall score, but its still nice to kinda mix things up.
When you have entered your coin, hold the first white key and the second black key on the 1p side, and rotate the turntable one rotation clock wise. Then, hold the third white and the first black key and rotate the turn table one rotation clockwise. Then hold the second black key, hit start, and quickly let go of the second black key and hold the first black key. If successful you should be able to select all songs on hard mode no matter what the difficulty is and what stage it is.