If you're just trying to visualize your data, have a look at Data::Dumper.

Otherwise, with a few modifications, your code works.

use strict;
use warnings;

use Data::Dumper;

my %ThreeD = (
              TV => {
                     version3 => {
                                  lead      => "fred",
                                  pal       => "barney",
                              },
                 },
          );

print Dumper( \%ThreeD );

# print the whole thing
foreach my $media ( keys %ThreeD) {
    print "$media @ {";
    for my $media_ver ( keys %{ $ThreeD{$media} } ) {
        print "$media_ver { ";
        for my $leaf_obj ( keys %{ $ThreeD{$media}{$media_ver} } ) {
            print "$leaf_obj=$ThreeD{$media}{$media_ver}{$leaf_obj} ";
        }
    }
    print "}\n";
}
__END__
$VAR1 = { 
          'TV' => { 
                    'version3' => { 
                                    'lead' => 'fred',
                                    'pal' => 'barney'
                                  }
                  }
        };
TV @ {version3 { lead=fred pal=barney }
[download]

Always use strict. It highlighted one of your errors for me. Specifically, you used $media_ver before it was defined. The other problem I found was just that your syntax for accessing the second level down was wrong (it's $ThreeD{$media}{$media_ver}).