Well, you have 140 million iterations of an operation, or a set of operations. My question is, how do you know whether it's still grinding along, and hasn't finished, versus it chokes and dies. You say it stops and the print never shows up. Well, does the program end, and you get your cursor back? My guess is that your program doesn't stop, it just keeps struggling to finish the loops, and you have nothing to tell you it's still working.

You might want to try adding a line in one of the earlier loops that prints something (even a period).

use strict;
use warnings;

my %hash = ();
foreach my $a (1..500) {
print "."; # <- Show we're alive by printing a dot...
    foreach my $b (1..4000) {
        foreach my $c (1..10) {
            foreach my $d (1..7) {
                $hash{$a}{$b}{$c}{$d} = $d;
            }
        }
    }
}
print "here\n";
[download]

Anyway, that's just my thoughts on it - YMMV.