open (FH,$ARGV[0]) or print "could not open file" ; 
# Better to use the 3-argument version of "open", and lexical file handles :
#   open ( my $fh, "<", $ARGV[0]) or print "could not open file '$ARGV[0]'; $!";
 
my $info = <FH>; # This reads ONLY the first line of the file..
# You need to put the file reading into a "while" loop that exits at EOF
# Typically, this is written : while (<$fh>){ ..do stuff .. }

while ($info=~ /(\w+ (-?\d+ )+)/)    # move regex stuff inside the while
{
        my $info =~ s/(\w+ (-?\d+ )+)//; # Careful with spaces inside regexs
}

my @nums = split(/:/,$info); # These need to be inside the while
my $word = shift (@nums);
my $sum = 0;
my $var = ($info);

foreach $var (@nums)  # Adding up stuff needs to be inside the while
{
    $sum = $sum + $var;
}


my %hash = ($word = $sum); # You mean ($word => $sum)

print @nums; # try print "@nums\n"; That will space out the numbers, and add a newline.