Your first problem is that your syntax for initialising a hash is wrong. It should be (at minimum):

%HASH   = (  # << note the parens not curlies.
        1  => \@ARRAY1,
        2  => \@ARRAY2,
        3  => \@ARRAY3,
        4  => \@ARRAY4,
          );
[download]

Take a look at References quick reference for the definitive guide to using references and come back with any specific questions that remain or arise.