There's a number of things you need to do:

• Separate the values in [ ... ] with commas or use [ qw{ ... } ]
• Access the values by dereferencing them: @{$Hash{$key}}
• Call next when the value is an empty list
• Change KEYS to KEY - you're only accessing one per loop iteration and stating KEYS could be confusing
• Add some formatting to get the output you want

Here's my code - it's only minimally changed from yours - check the notes above.

#!perl

use 5.12.0;
use warnings;

my %Hash = (
    'acer.xml' => [],
    'tools.xml' => [],
    'files.xml' => [ 'organize/file/load.c#6','embark/files/data.c#4' 
+],
    'multimedia.xml' => [],
    'extra_for_test.xml' => [ qw{ blahA blahB blahC } ],
);

foreach my $key ( keys %Hash ) {
        next unless @{$Hash{$key}};
        my $value = join "\n\t", @{$Hash{$key}};
        print "KEY:\t$key\nVALUES:\t$value\n";
}
[download]

And here's the output:

$ xml_hash_prob.pl
KEY:    extra_for_test.xml
VALUES: blahA
        blahB
        blahC
KEY:    files.xml
VALUES: organize/file/load.c#6
        embark/files/data.c#4
[download]